Soma-notes - User contributions [en]

COMP 3000 Essay 2 2010 Question 7

2010-12-01T19:04:53Z

Slay: /* Findings */

==Paper==
===[http://homeostasis.scs.carleton.ca/wiki/index.php/COMP_3000_Essay_2_2010_Question_7 Ad Hoc Synchronization Considered Harmful]===
Weiwei Xiong
University of California, San Diego

Soyeon Park, Jiaqi Zhang, Yuanyuan Zhou
University of Illinois at Urbana-Champaign

Zhiqiang Ma
Intel

==Research Problem==
As the computer industry continues to shift towards multicore processors, concurrent programming and the use of multithreaded designs has increased to keep up with this growing trend. Multithreaded applications can be found in a variety of popular applications today as they take advantage of the multithreaded approach. However, the concepts behind concurrent programming bring with them a host of potential dangers in the form of race conditions and deadlocks resulting from bad programming design and threads accessing shared memory. Fortunately, there are well known and standard methods for dealing with these problems, i.e synchronization primitives. But in real world situations, due to a variety of reasons, as we shall see, programmers often implement their own "ad hoc" synchronizations that eschew common design standards. Ad hoc synchronizations are not well documented and are not discovered by traditional tools for race conditions that look for standard synchronization primitives.

The paper we are discussing addresses these concerns in two regards, first it details a thorough study of ad hoc synchronizations. It details their nature, dangers, impact on bug detection tools and prevalence in several major open-source applications. Secondly, it introduces SyncFinder, a program that detects all ad hoc synchronizations and automatically annotates the source code where ad hoc sychnronizations are found. This can see use in conjunction with other data race checkers to improve accuracy and to build custom tools for finding deadlocks and bad programming practices.

With detailed analysis of ad hoc synchronization and study of their occurrences in several applications, the research ultimately concludes that they are harmful and should be removed. At the same time, SyncFinder detects and documents ad hoc synchronizations in the source code enabling programmers for the first time to easily track and remove them.

==Background Concepts==

===Concurrent Programming===
Concurrent programming is a style of programming where multiple threads of execution run concurrently to perform a single task. The thread of execution share a number of resources. Particularly in multi-core processor system and in distributed environment this style of programming can result in significant performance gains. One significant challenge of concurrent programming is coordinating the different threads of execution, this is usually done using synchronization primitives.

===Synchronization Primitives===
Synchronization primitives represent some of the basic tools offered by the system containing the concurrent program to facilitate coordination between of threads of execution. They are generally used to synchronize between threads, and to protect shared resource[[#Foot8|8]].
Some type of synchronization primitives common to many are locks, mutexes, semaphores, and monitors.
Locks are really a superset of synchronization primitives since mutexes, semaphores, and monitors are all locks. Additionally there are read/write locks that only lock when a reader obtains the lock. Latches a type of lock that unlocks when a specified number of threads have obtained it which is very useful in facilitate threads all getting to known state, there are a myriad of other locks.
Mutexes are mutually exclusive locks that threads employ to lock a resource that they need preventing other. No other threads can access them at that point. Once they are finished, they release the lock and the other threads can then lock and access the resource.
Monitors are a type of mutex that contain a condition variables which is a variable that if not true, releases the lock and blocks the thread until the certain condition is met, by another thread changing value of the variable. This allows the original thread to only continue execute when it is safe to perform its operation.
Synchronization primitives can be misused and lead to a host of other problems generally referred to collectively as race conditions.
===Race conditions, deadlocks===
Race conditions are an unintended side-effects of programming in concurrent systems, they occur when two or more processes have access to a shared resource and at least one of them have write privilege. This leads to processes modifying the data that all processes share as other may be reading them and results in the reading of stale/incorrect data. They will occur during the execution of the program and often times very difficult to detect or manipulate data in subtle ways.

Deadlock is when two or more processes share a resource and each process is waiting on the other processes to unlock the resource. It becomes a circular chain and no process can continue.

Both these issues occur in concurrent programming and although there are no general solutions for deadlock[[#Foot9|9]], there are suitable methods for dealing with them, and in the case of race conditions, using mutual exclusion locks and synchronization primitives can prevent race conditions. But no programmer is infallible and so there is always the issue of race conditions and deadlocks present in production code.
===Ad Hoc Synchronization===
Ad hoc synchronizations are loops called sync loops that continue until certain conditions are met via outside variables called sync variables. They are designed to control the flow of thread execution much like locking and unlocking of resources. There can be multiple sync variables in a sync loop and they can have multiple exit conditions and dependencies. The diversity of the sync loops, their dependencies and execution paths leads to difficulty in finding them.

==Contribution==

With concurrent programming commonly used in modern applications, we face many issues that result from having simultaneous execution. In order to maintain a concurrent system, synchronization is required to ensure that the executing tasks do not interfere with each other avoiding potential race conditions. However, many programmers do not use proper synchronization primitives to deal with these issues. Rather, they implement synchronizations in an ad hoc fashion. The paper we are discussing shows that ad hoc synchronizations, though implemented as a solution to concurrency issues, are indeed undesirable in a system. This paper details the characteristics of ad hoc synchronizations and the issues associated with this programming construct and introduces the program, SyncFinder, which is used to identify such synchronizations in code.

===Findings===

In order to identify the characteristics of ad hoc synchronizations, 12 mainstream programs were examined to find instances of ad hoc synchronizations. These programs were either of server, desktop or scientific type, including Apache, MySQL and Mozilla. Through manual inspection of the source code, these characteristics of ad hoc synchronizations were found.

1. In all programs studied, it was found that each had numerous ad hoc synchronizations implemented. The number of synchronizations found ranged from 6-83, with server type programs inhabiting the higher portion of the interval. It is likely that programmers use this type of synchronization for two reasons.
* In order to ensure a certain order of execution in the case of a concurrent system, programmers will use ad hoc synchronization to superimpose this order. With traditional synchronization techniques, this can vary between systems. As the order can vary, it is difficult to create a common interface.
* Some synchronization techniques introduce heavy-weight synchronization primitives. As such, programmers will use ad hoc synchronizations to avoid this and supposedly protect performance.

2. Often, it is very hard to identify an ad hoc loop as a synchronization method. They are hard to distinguish from other computational loops and as the implementations are diverse, it is hard to pinpoint them from the code. This makes the system hard to maintain, as other programmers will not be able to identify ad hoc loops implemented by another and debugging programs cannot recognize them as issues.

3. It was found that ad hoc synchronizations often introduce bugs into the system such as deadlocks or hangs. As these are different than those caused by locks and other synchronizations it is hard for detection tools to recognize them if they were not first identified either manually or automatically.

4. As they are not easily recognizable, it is hard for bug detection tools to fix issues presented by ad hoc synchronizations. In fact, it is often the case that these tools either do not find these issues or report them as false positives as the tool is unaware of the "work arounds" put into affect by using ad hoc synchronization. Since they cannot find these problems, it severely impacts the effectiveness of such tools.
This also impacts analysis of performance. Synchronization is quite costly and if a tool cannot recognize the formm of synchronization, a false report is generated and the programmer will not be aware. This may cause poor decisions on the part of the programmer just from the fact that ad hoc synchronizations are hard to identify.

5. The reason ad hoc synchronizations are hard to identify stems from the fact that there is no single way of implementing it. The ways in which ad hoc synchronizations are done are quite diverse and so it is hard to identify just on a few criteria. Some typical characteristics of an ad hoc synchronization follow.
* These loops can contain one or multiple exit conditions. Some or all of these exit conditions may be satisfied by remote threads while others may be satisfied locally.
* Often, exit conditions depend on sync variables, variables that are shared with other tasks
* In some cases, the synchronization does not wait idly and rather performs other computations while checking the sync variable periodically

Despite the dangers of using ad hoc synchronization, programmers continue to use this method. It is found that, in comments, programmers have stated that possibly their implementations are unsafe but proceed to use ad hoc synchronization techniques. The reasoning behind these decisions have already been outlined in point 1. A better practice of synchronization would be to replace ad hoc synchronizations with synchronization primitives, primitives already present in standard POSIX thread libraries. However, it is often difficult to replace ad hoc synchronizations with synchronization primitives and doing this may not fulfill the concerns presented in point 1.

===SyncFinder===
SyncFinder is a tool built and designed by the authors of the paper for the purpose of identifying and annotating instances of ad hoc synchronization in concurrent programs built in C or C++. The main goal of this was to aid programmers in better structuring their code, while simultaneously allowing for other tools to be utilized, recognizing them as synchronizations. It has demonstrated itself to be very effective in this area where other similar tools have failed, as it analyzes the code in a unique way that specifically tracks down sync loops that implement ad hoc synchronization.

====How it works====
There are two possibilities to consider when searching for ad hoc synchronizations. You can either analyze runtime traces via a dynamic method, or analyze the source code in a static method. Both methods carry with them a number of pros and cons. While a dynamic process is generally more accurate than a static method, it tends to accrue a very large runtime overhead. In addition to this, the dynamic method is somewhat limited in which ad hoc synchronizations it can find by the code coverage of the test cases. Taking these factors into consideration, the authors of the paper opted to pursue a static solution for achieving the goals set out for SyncFinder. SyncFinder uses the LLVM compiler infrastructure.

1. Find Loops

An important commonality between all ad hoc synchronizations is that they are all caused by loops, be they “for”, “while” or “go to” loops. These are generally referred to as "sync loops". The first step in identifying sync loops is The LLVM infrastructure is used to obtain the loop info from the source including a representation of the exit conditions.

2. Identify Sync Loops

The next and most important step is to differentiate between sync loops used for ad hoc synchronization and regular computational loops. It does this by going through the following steps:
* Exit Dependent Variable (EDV) Analysis: EDVs are variables that affect the exit conditions of a loop. A sync variable is a variable related to the synchronization of concurrent programs. Therefore, by identifying any EDVs as sync variables, it can be concluded that the loop is a sync loop.
* Pruning Computational Loops: If a loop has at least one sync condition, it is considered a sync loop. Otherwise, it is pruned out as a computational loop.
* Pruning Condvar Loops: condvar loops are not considered sync loops. SyncFinder will go through all loop candidates and prune out any that make a calls cond_wait inside the loop.

3. Synchronization Pairing

The next step is to find the remote update that would release the sync loop. SyncFinder first finds all write instructions that would modify the sync variables. It then decides if the value that the write assigns to the sync variable would satisfy the exit condition. All those that do not are pruned. SyncFinder also prunes pairings that do not execute concurrently. This is done conservatively due to the limitations of static analysis.

4. SyncFinder Annotation

Finally, SyncFinder annotates these ad hoc synchronizations in a specific way so that other tools are able to find them.

====Uses====
SyncFinder is a robust tool that can be utilized in a variety of applications such as bug detection, performance profiling and concurrency testing. Using its auto-annotation feature, it is capable of identifying sections of code that demonstrate bad programming practices, which could in turn cause issues such as deadlocks. In addition to this, the authors of the paper were able to expand upon the existing data race detector “Valgrind” in order to take advantage of the annotation system introduced by SyncFinder. Through this, they were able to reduce the number of false positives flagged by the former, while being able to make use of the information it provides.

====Accuracy====
SyncFinder was tested against 25 concurrent programs that are used across a broad cross-section of application. In testing SyncFinder was able to positively identify 96% of ad hoc synchronizations within the tested programs. False positives were at a rate of only 6%. In further tests, they were able to utilize SyncFinder’s auto-annotation systems to locate and mark 5 deadlocks and 16 potential issues within Apache, MySQL and Mozilla, that had previously been missed by other analysis tools.

====Related Work and similar tools====
There has been attempts to remove synchronization issues entirely from concurrent programming, such as transactional memory[[#Foot1|1]], a lock-free synchronization that does not require mutexes, and avoids having to use lock, unlock operations. Other attempts have been made to remove bugs that would otherwise be safe from data races but are are still at risk of unintended effects from thread interactions, such as Atomizer[[#Foot2|2]], a dynamic atomicity checker.

There are tools that detect data races such as CHESS[[#Foot3|3]], a dynamic data race checker that runs through all possible thread execution paths and CTrigger[[#Foot4|4]], a tool that checks for atomicity violations. The problem with these programs is that they only look for standard synchronization methods and structures, such as lock() and cond_wait(). They are not looking for ad hoc synchronizations.

A similar tool to SyncFinder exists that can detect simple spinning, also an ad hoc synchronization[[#Foot5|5]], but it only detects simple spinning and not the more complicated ad hoc variations.

Several studies on bug characteristics[[#Foot6|6]] and concurrency bugs[[#Foot7|7]] have been composed. This paper complements these studies to better understand the nature of ad hoc synchronizations and their occurrence in concurrent programs.

==Critique==
1. Uses static approach, dynamic would be better
* As stated in the paper, dynamic introduces run-time overhead and is not guaranteed to find if not executed in the test cases
Dynamic would potentially make it language agnostic.

2. not entirely accurate, some false positives.

3. In terms of style, lots of unnecessary repetition

This paper successfully identifies a new type programming construct ad hoc synchronization. The paper then refers to a body of data that the authors have created that both provides proof of the criteria to identify the construct and illustrates it's frequency and likelihood to introduce bugs. Previous to SyncFinder, debugging tools have for the most part failed to detect ad hoc synchronizations effectively. Because of this, SyncFinder has been shown to be an important tool for future development of software.

As far as shortcomings go, it has a 96% success rate, with 6% false positives. The 6% false positive rate is more or less unavoidable, so it is hard to fault the tool for that, especially with such a high success rate. Even with a 6% false positive rate, the developer still only needs to look through a select few loops to determine which are actually ad hoc synchronizations as opposed to a whole code base.

Finally the tool that the authors have created has been used on ubiquitous applications[[#Foot10|10]] like Apache and exposed previously unreported bugs. This stands as a testament to both it's effectiveness and validity.

==References==
1 M Herlihy and J.E.B. Moss, 2NA0. Transactional Memory:
Architectural Support for Lock-Free Data Structures. [online] Available at: <http://www.cs.brown.edu/~mph/HerlihyM93/herlihy93transactional.pdf> [Accessed 23 November 2010].

2 C Flanagan and S N Freund, 2NA0. Atomizer: A Dynamic Atomicity Checker For Multithreaded Programs (Summary). [online] Company(optional) Available at: <http://www.cs.williams.edu/~freund/papers/atomizer-padtad.pdf> [Accessed 23 November 2010].

3 T Ball,M Musuvathi and S Qadeer, 2NA0. CHESS: A Systematic Testing Tool for Concurrent. [online] Company(optional) Available at: <http://research.microsoft.com/pubs/70509/tr-2007-149.pdf> [Accessed 23 November 2010].

4 Author, 2NA0. Title. [online] Company(optional) Available at: <http://pages.cs.wisc.edu/~shanlu/paper/asplos092-zhou.pdf> [Accessed 23 November 2010].

5 LI, T., LEBECK, A. R., AND SORIN, D. J. Spin detection hardware for improved management of multithreaded systems. IEEE Transactions on Parallel and Distributed Systems PDS-17, 6 (June 2006), 508–521.

6 Author, 2NA0. Title. [online] Company(optional) Available at: <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf> [Accessed 23 November 2010].

7 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf]> [Accessed 23 November 2010].

8 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://www.usenix.org/events/bsdcon/full_papers/baldwin/baldwin_html/node5.html]> [Accessed 23 November 2010].

9 Author, 2010. Title. [online] Company(optional) Available at: <http://homeostasis.scs.carleton.ca/wiki/index.php/Basic_Synchronization_Principles> [Accessed 23 November 2010].

10 Author, 2010. Title. [online] Company(optional) Available at: <http://trends.builtwith.com/Web-Server/Apache> [Accessed 30 November 2010].

Talk:COMP 3000 Essay 2 2010 Question 7

2010-11-28T00:28:08Z

Slay:

'''Attendence. Please mark your name to say you're here'''

Stephany Lay --[[User:Slay|Slay]] 19:45, 15 November 2010 (UTC)

--[[User:Asoknack|Asoknack]] 16:00, 15 November 2010 (UTC)

--[[User:Smcilroy|Smcilroy]] 18:43, 15 November 2010 (UTC)

Lester Mundt
--[[User:Lmundt|Lmundt]] 18:58, 15 November 2010 (UTC)

Thomas McMahon
--[[User:cha0s|cha0s]]

Martin Kugler
--[[User:Mkugler|Mkugler]] 02:42, 18 November 2010 (UTC)

So only 2 days left before it's due! I'd like to hear what others are planning on contributing and when, since only myself and Slay have done any work on the actual essay. It would be nice to hear from you guys, even if its to say that your busy and are going to work on it on Thursday etc. etc.--[[User:Smcilroy|Smcilroy]] 22:05, 23 November 2010 (UTC)

So, what's the plan for this? How do we want to do this? Given the duedate looming in 4 days we should probably get talking about it. What are your thoughts?
--[[User:Mkugler|Mkugler]] 23:00, 21 November 2010 (UTC)
::Hey! So I added an intro and it covers the research problem to. I also added a bare bones skeleton of what we'll probably end up talking about. Personally, I think people should choose a couple of subsections and sections that they will work on and just put your name beside it. It seems to work best as people then have a sense of ownership and responsibility to that particular topic and aren't overwhelmed at editing the entire essay, at least for the beginning. That doesn't mean we can't all edit each others work though! I welcome any changes to the intro. Anyways, that's my 2 cents. --[[User:Smcilroy|Smcilroy]] 06:06, 22 November 2010 (UTC)
::As critique is our own opinion, we should discuss our thoughts. Having only one person writing that would not express everyone's opinions. --[[User:Slay|Slay]] 20:48, 22 November 2010 (UTC)

Hey, gonna be fleshing out the Contribution section, probably the stuff under the SyncFinder heading. Just wanted to give people a head's up so we don't waste time all doing the same thing.
--[[User:Mkugler|Mkugler]] 03:09, 24 November 2010 (UTC)

I will do the Findings section for now then. I'm unsure when I'll get to it though. I'll try for this weekend. --[[User:Slay|Slay]] 00:14, 26 November 2010 (UTC)

Not much activity going on. Please at least claim a section to work on so we know it will get covered. I'll continue to work on my part when I get the time. --[[User:Slay|Slay]] 00:28, 28 November 2010 (UTC)

COMP 3000 Essay 2 2010 Question 7

2010-11-28T00:26:06Z

Slay:

==Paper==
===Ad Hoc Synchronization Considered Harmful===
Weiwei Xiong
University of California, San Diego

Soyeon Park, Jiaqi Zhang, Yuanyuan Zhou
University of Illinois at Urbana-Champaign

Zhiqiang Ma
Intel
==Research Problem==
As the computer industry continues to shift towards multicore processors, concurrent programming and the use of multithreaded designs has increased to keep up with this growing trend. Multithreaded applications can be found in a variety of popular applications today as they take advantage of the multithreaded approach. However, the concepts behind concurrent programming bring with them a host of potential dangers in the form of race conditions and deadlocks resulting from bad programming design and threads accessing shared memory. Fortunately, there are well known and standard methods for dealing with these problems, i.e synchronization primitives. But in real world situations, due to a variety of reasons, as we shall see, programmers often implement their own "ad hoc" synchronizations that eschew common design standards. Ad hoc synchronizations are not well documented and are not discovered by traditional tools for race conditions that look for standard synchronization primitives.

This paper addresses these concerns in two regards, first it details a thorough study of ad hoc synchronizations. It details their nature, dangers, impact on bug detection tools and prevalence in several major open-source applications. Secondly, it introduces SyncFinder, a program that detects all ad hoc synchronizations and automatically annotates the source code where ad hoc sychnronizations are found. This can see use in conjunction with other data race checkers to improve accuracy and to build custom tools for finding deadlocks and bad programming practices.

With detailed analysis of ad hoc synchronization and study of their occurrences in several applications, the research ultimately concludes that they are harmful and should be removed. At the same time, SyncFinder detects and documents ad hoc synchronizations in the source code enabling programmers for the first time to easily track and remove them.

==Background Concepts==
===Race conditions, deadlocks===
Race conditions are an unintended side-effects of programming in concurrent systems, they occur when two or more processes have access to a shared resource and at least one of them have write privilege. This leads to processes modifying the data that all processes share as other may be reading them and results in the reading of stale/incorrect data. They will occur during the execution of the program and often times very difficult to detect or manipulate data in subtle ways.

Deadlock is when two or more processes share a resource and each process is waiting on the other processes to unlock the resource. It becomes a circular chain and no process can continue.

Both these issues occur in concurrent programming and although there are no general solutions for deadlock[[#Foot9|9]], there are suitable methods for dealing with them, and in the case of race conditions, using mutual exclusion locks and synchronization primitives can prevent race conditions. But no programmer is infallible and so there is always the issue of race conditions and deadlocks present in production code.
===Ad Hoc Synchronization===
Ad hoc synchronizations are loops called sync loops that continue until certain conditions are met via outside variables called sync variables. They are designed to control the flow of thread execution much like locking and unlocking of resources. There can be multiple sync variables in a sync loop and they can have multiple exit conditions and dependencies. The diversity of the sync loops, their dependencies and execution paths leads to difficulty in finding them.
===Synchronization primitives===
Synchronization variables act as barriers to memory that prevent threads from accessing the same shared resource concurrently[[#Foot8|8]]. They come in many forms such as mutexes and condition variables.
Mutexes are mutual exclusive locks that threads employ to lock a resource that they need. No other threads can access them at that point. Once they are finished, they release the lock and the other threads can then lock and access the resource.
Condition variables are variables that will block the thread until a certain condition is met. This allows the thread to only execute when it is safe to perform its operation.

==Contribution==

With concurrent programming commonly used in modern applications, we face many issues that result from having simultaneous execution. In order to maintain a concurrent system, synchronizations are required to ensure that the executing tasks do not interfere with each other, which could be disastrous for the system. However, many programmers do not use proper synchronization techniques to deal with these issues. Rather, they implement synchronizations in an ad hoc fashion. In this study, it is shown that ad hoc synchronizations, though implemented as a solution to concurrency issues, are indeed undesirable in a system. This paper details the characteristics of ad hoc synchronizations and the issues associated with this implementation and introduces the program, SyncFinder, which is used to identify such synchronizations in code.

===Findings===

In order to identify the characteristics of ad hoc synchronizations, 12 mainstream programs were examined to find instances of ad hoc synchronizations. These programs were either of server, desktop or scientific type, including Apache, MySQL and Mozilla. Through manual inspection of the source code, these characteristics of ad hoc synchronizations were found.

1. In all programs studied, it was found that each had numerous ad hoc synchronizations implemented. The number of synchronizations found ranged from 6-83, with server type programs inhabiting the higher portion of the interval. It is likely that programmers use this type of synchronization for two reasons.
* In order to ensure a certain order of execution in the case of a concurrent system, programmers will use ad hoc synchronization to superimpose this order. With traditional synchronization techniques, this can vary between systems. As the order can vary, it is difficult to create a common interface.
* Some synchronization techniques introduce heavy-weight synchronization primitives. As such, programmers will use ad hoc synchronizations to avoid this and supposedly protect performance.

2. Often, it is very hard to identify an ad hoc loop as a synchronization method. They are hard to distinguish from other computational loops and as the implementations are diverse, it is hard to pinpoint them from the code. This makes the system hard to maintain, as other programmers will not be able to identify ad hoc loops implemented by another and debugging programs cannot recognize them as issues.

3. It was found that ad hoc synchronizations often introduce bugs into the system such as deadlocks or hangs. As these are different than those caused by locks and other synchronizations it is hard for detection tools to recognize them if they were not first identified either manually or automatically.

4. As they are not easily recognizable, it is hard for bug detection tools to fix issues presented by ad hoc synchronizations. In fact, it is often the case that these tools either do not find these issues or report them as false positives as the tool is unaware of the "work arounds" put into affect by using ad hoc synchronization. Since they cannot find these problems, it severely impacts the effectiveness of such tools.
This also impacts analysis of performance. Synchronization is quite costly and if a tool cannot recognize the formm of synchronization, a false report is generated and the programmer will not be aware. This may cause poor decisions on the part of the programmer just from the fact that ad hoc synchronizations are hard to identify.

5. The reason ad hoc synchronizations are hard to identify stems from the fact that there is no single way of implementing it. The ways in which ad hoc synchronizations are done are quite diverse and so it is hard to identify just on a few criteria. Some typical characteristics of an ad hoc synchronization follow.
* These loops can contain one or multiple exit conditions. Some or all of these exit conditions may be satisfied by remote threads while others may be satisfied locally.
* [working on it]

Reasons behind why people use ad hoc synchronization and possible improvements over them ie Synchronization primitives

===SyncFinder===
Intro to what it is and what it does
====How it works====
1. find loops

2. identify sync loops

3. EDV analysis

4. Pruning

5. Annotation of found sync

====Uses====
1. A tool to detect bad practices

2. Extensions to data race detection

====Accuracy====

====Related Work and similar tools====
There has been attempts to remove synchronization issues entirely from concurrent programming, such as transactional memory[[#Foot1|1]], a lock-free synchronization that does not require mutexes, and avoids having to use lock, unlock operations. Other attempts have been made to remove bugs that would otherwise be safe from data races but are are still at risk of unintended effects from thread interactions, such as Atomizer[[#Foot2|2]], a dynamic atomicity checker.

There are tools that detect data races such as CHESS[[#Foot3|3]], a dynamic data race checker that runs through all possible thread execution paths and CTrigger[[#Foot4|4]], a tool that checks for atomicity violations. The problem with these programs is that they only look for standard synchronization methods and structures, such as lock() and cond_wait(). They are not looking for ad hoc synchronizations.

A similar tool to SyncFinder exists that can detect simple spinning, also an ad hoc synchronization[[#Foot5|5]], but it only detects simple spinning and not the more complicated ad hoc variations.

Several studies on bug characteristics[[#Foot6|6]] and concurrency bugs[[#Foot7|7]] have been composed. This paper complements these studies to better understand the nature of ad hoc synchronizations and their occurrence in concurrent programs.

==Critique==
1. Uses static approach, dynamic would be better
* As stated in the paper, dynamic introduces run-time overhead and is not guaranteed to find if not executed in the test cases

2. not entirely accurate, some false positives.

3. In terms of style, lots of unnecessary repetition

==References==
1 M Herlihy and J.E.B. Moss, 2NA0. Transactional Memory:
Architectural Support for Lock-Free Data Structures. [online] Available at: <http://www.cs.brown.edu/~mph/HerlihyM93/herlihy93transactional.pdf> [Accessed 23 November 2010].

2 C Flanagan and S N Freund, 2NA0. Atomizer: A Dynamic Atomicity Checker For Multithreaded Programs (Summary). [online] Company(optional) Available at: <http://www.cs.williams.edu/~freund/papers/atomizer-padtad.pdf> [Accessed 23 November 2010].

3 T Ball,M Musuvathi and S Qadeer, 2NA0. CHESS: A Systematic Testing Tool for Concurrent. [online] Company(optional) Available at: <http://research.microsoft.com/pubs/70509/tr-2007-149.pdf> [Accessed 23 November 2010].

4 Author, 2NA0. Title. [online] Company(optional) Available at: <http://pages.cs.wisc.edu/~shanlu/paper/asplos092-zhou.pdf> [Accessed 23 November 2010].

5 LI, T., LEBECK, A. R., AND SORIN, D. J. Spin detection hardware for improved management of multithreaded systems. IEEE Transactions on Parallel and Distributed Systems PDS-17, 6 (June 2006), 508–521.

6 Author, 2NA0. Title. [online] Company(optional) Available at: <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf> [Accessed 23 November 2010].

7 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf]> [Accessed 23 November 2010].

8 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://www.usenix.org/events/bsdcon/full_papers/baldwin/baldwin_html/node5.html]> [Accessed 23 November 2010].

9 Author, 2010. Title. [online] Company(optional) Available at: <http://homeostasis.scs.carleton.ca/wiki/index.php/Basic_Synchronization_Principles> [Accessed 23 November 2010].

COMP 3000 Essay 2 2010 Question 7

2010-11-28T00:25:32Z

Slay:

==Paper==
===Ad Hoc Synchronization Considered Harmful===
Weiwei Xiong
University of California, San Diego

Soyeon Park, Jiaqi Zhang, Yuanyuan Zhou
University of Illinois at Urbana-Champaign

Zhiqiang Ma
Intel
==Research Problem==
As the computer industry continues to shift towards multicore processors, concurrent programming and the use of multithreaded designs has increased to keep up with this growing trend. Multithreaded applications can be found in a variety of popular applications today as they take advantage of the multithreaded approach. However, the concepts behind concurrent programming bring with them a host of potential dangers in the form of race conditions and deadlocks resulting from bad programming design and threads accessing shared memory. Fortunately, there are well known and standard methods for dealing with these problems, i.e synchronization primitives. But in real world situations, due to a variety of reasons, as we shall see, programmers often implement their own "ad hoc" synchronizations that eschew common design standards. Ad hoc synchronizations are not well documented and are not discovered by traditional tools for race conditions that look for standard synchronization primitives.

This paper addresses these concerns in two regards, first it details a thorough study of ad hoc synchronizations. It details their nature, dangers, impact on bug detection tools and prevalence in several major open-source applications. Secondly, it introduces SyncFinder, a program that detects all ad hoc synchronizations and automatically annotates the source code where ad hoc sychnronizations are found. This can see use in conjunction with other data race checkers to improve accuracy and to build custom tools for finding deadlocks and bad programming practices.

With detailed analysis of ad hoc synchronization and study of their occurrences in several applications, the research ultimately concludes that they are harmful and should be removed. At the same time, SyncFinder detects and documents ad hoc synchronizations in the source code enabling programmers for the first time to easily track and remove them.

==Background Concepts==
===Race conditions, deadlocks===
Race conditions are an unintended side-effects of programming in concurrent systems, they occur when two or more processes have access to a shared resource and at least one of them have write privilege. This leads to processes modifying the data that all processes share as other may be reading them and results in the reading of stale/incorrect data. They will occur during the execution of the program and often times very difficult to detect or manipulate data in subtle ways.

Deadlock is when two or more processes share a resource and each process is waiting on the other processes to unlock the resource. It becomes a circular chain and no process can continue.

Both these issues occur in concurrent programming and although there are no general solutions for deadlock[[#Foot9|9]], there are suitable methods for dealing with them, and in the case of race conditions, using mutual exclusion locks and synchronization primitives can prevent race conditions. But no programmer is infallible and so there is always the issue of race conditions and deadlocks present in production code.
===Ad Hoc Synchronization===
Ad hoc synchronizations are loops called sync loops that continue until certain conditions are met via outside variables called sync variables. They are designed to control the flow of thread execution much like locking and unlocking of resources. There can be multiple sync variables in a sync loop and they can have multiple exit conditions and dependencies. The diversity of the sync loops, their dependencies and execution paths leads to difficulty in finding them.
===Synchronization primitives===
Synchronization variables act as barriers to memory that prevent threads from accessing the same shared resource concurrently[[#Foot8|8]]. They come in many forms such as mutexes and condition variables.
Mutexes are mutual exclusive locks that threads employ to lock a resource that they need. No other threads can access them at that point. Once they are finished, they release the lock and the other threads can then lock and access the resource.
Condition variables are variables that will block the thread until a certain condition is met. This allows the thread to only execute when it is safe to perform its operation.

==Contribution==

With concurrent programming commonly used in modern applications, we face many issues that result from having simultaneous execution. In order to maintain a concurrent system, synchronizations are required to ensure that the executing tasks do not interfere with each other, which could be disastrous for the system. However, many programmers do not use proper synchronization techniques to deal with these issues. Rather, they implement synchronizations in an ad hoc fashion. In this study, it is shown that ad hoc synchronizations, though implemented as a solution to concurrency issues, are indeed undesirable in a system. This paper details the characteristics of ad hoc synchronizations and the issues associated with this implementation and introduces the program, SyncFinder, which is used to identify such synchronizations in code.

===Findings===

In order to identify the characteristics of ad hoc synchronizations, 12 mainstream programs were examined to find instances of ad hoc synchronizations. These programs were either of server, desktop or scientific type, including Apache, MySQL and Mozilla. Through manual inspection of the source code, these characteristics of ad hoc synchronizations were found.

# In all programs studied, it was found that each had numerous ad hoc synchronizations implemented. The number of synchronizations found ranged from 6-83, with server type programs inhabiting the higher portion of the interval. It is likely that programmers use this type of synchronization for two reasons.
* In order to ensure a certain order of execution in the case of a concurrent system, programmers will use ad hoc synchronization to superimpose this order. With traditional synchronization techniques, this can vary between systems. As the order can vary, it is difficult to create a common interface.
* Some synchronization techniques introduce heavy-weight synchronization primitives. As such, programmers will use ad hoc synchronizations to avoid this and supposedly protect performance.

# Often, it is very hard to identify an ad hoc loop as a synchronization method. They are hard to distinguish from other computational loops and as the implementations are diverse, it is hard to pinpoint them from the code. This makes the system hard to maintain, as other programmers will not be able to identify ad hoc loops implemented by another and debugging programs cannot recognize them as issues.

# It was found that ad hoc synchronizations often introduce bugs into the system such as deadlocks or hangs. As these are different than those caused by locks and other synchronizations it is hard for detection tools to recognize them if they were not first identified either manually or automatically.

# As they are not easily recognizable, it is hard for bug detection tools to fix issues presented by ad hoc synchronizations. In fact, it is often the case that these tools either do not find these issues or report them as false positives as the tool is unaware of the "work arounds" put into affect by using ad hoc synchronization. Since they cannot find these problems, it severely impacts the effectiveness of such tools.
This also impacts analysis of performance. Synchronization is quite costly and if a tool cannot recognize the formm of synchronization, a false report is generated and the programmer will not be aware. This may cause poor decisions on the part of the programmer just from the fact that ad hoc synchronizations are hard to identify.

# The reason ad hoc synchronizations are hard to identify stems from the fact that there is no single way of implementing it. The ways in which ad hoc synchronizations are done are quite diverse and so it is hard to identify just on a few criteria. Some typical characteristics of an ad hoc synchronization follow.
* These loops can contain one or multiple exit conditions. Some or all of these exit conditions may be satisfied by remote threads while others may be satisfied locally.
* [working on it]

Reasons behind why people use ad hoc synchronization and possible improvements over them ie Synchronization primitives

===SyncFinder===
Intro to what it is and what it does
====How it works====
1. find loops

2. identify sync loops

3. EDV analysis

4. Pruning

5. Annotation of found sync

====Uses====
1. A tool to detect bad practices

2. Extensions to data race detection

====Accuracy====

====Related Work and similar tools====
There has been attempts to remove synchronization issues entirely from concurrent programming, such as transactional memory[[#Foot1|1]], a lock-free synchronization that does not require mutexes, and avoids having to use lock, unlock operations. Other attempts have been made to remove bugs that would otherwise be safe from data races but are are still at risk of unintended effects from thread interactions, such as Atomizer[[#Foot2|2]], a dynamic atomicity checker.

There are tools that detect data races such as CHESS[[#Foot3|3]], a dynamic data race checker that runs through all possible thread execution paths and CTrigger[[#Foot4|4]], a tool that checks for atomicity violations. The problem with these programs is that they only look for standard synchronization methods and structures, such as lock() and cond_wait(). They are not looking for ad hoc synchronizations.

A similar tool to SyncFinder exists that can detect simple spinning, also an ad hoc synchronization[[#Foot5|5]], but it only detects simple spinning and not the more complicated ad hoc variations.

Several studies on bug characteristics[[#Foot6|6]] and concurrency bugs[[#Foot7|7]] have been composed. This paper complements these studies to better understand the nature of ad hoc synchronizations and their occurrence in concurrent programs.

==Critique==
1. Uses static approach, dynamic would be better
* As stated in the paper, dynamic introduces run-time overhead and is not guaranteed to find if not executed in the test cases

2. not entirely accurate, some false positives.

3. In terms of style, lots of unnecessary repetition

==References==
1 M Herlihy and J.E.B. Moss, 2NA0. Transactional Memory:
Architectural Support for Lock-Free Data Structures. [online] Available at: <http://www.cs.brown.edu/~mph/HerlihyM93/herlihy93transactional.pdf> [Accessed 23 November 2010].

2 C Flanagan and S N Freund, 2NA0. Atomizer: A Dynamic Atomicity Checker For Multithreaded Programs (Summary). [online] Company(optional) Available at: <http://www.cs.williams.edu/~freund/papers/atomizer-padtad.pdf> [Accessed 23 November 2010].

3 T Ball,M Musuvathi and S Qadeer, 2NA0. CHESS: A Systematic Testing Tool for Concurrent. [online] Company(optional) Available at: <http://research.microsoft.com/pubs/70509/tr-2007-149.pdf> [Accessed 23 November 2010].

4 Author, 2NA0. Title. [online] Company(optional) Available at: <http://pages.cs.wisc.edu/~shanlu/paper/asplos092-zhou.pdf> [Accessed 23 November 2010].

5 LI, T., LEBECK, A. R., AND SORIN, D. J. Spin detection hardware for improved management of multithreaded systems. IEEE Transactions on Parallel and Distributed Systems PDS-17, 6 (June 2006), 508–521.

6 Author, 2NA0. Title. [online] Company(optional) Available at: <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf> [Accessed 23 November 2010].

7 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf]> [Accessed 23 November 2010].

8 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://www.usenix.org/events/bsdcon/full_papers/baldwin/baldwin_html/node5.html]> [Accessed 23 November 2010].

9 Author, 2010. Title. [online] Company(optional) Available at: <http://homeostasis.scs.carleton.ca/wiki/index.php/Basic_Synchronization_Principles> [Accessed 23 November 2010].

COMP 3000 Essay 2 2010 Question 7

2010-11-27T23:03:39Z

Slay:

==Paper==
===Ad Hoc Synchronization Considered Harmful===
Weiwei Xiong
University of California, San Diego

Soyeon Park, Jiaqi Zhang, Yuanyuan Zhou
University of Illinois at Urbana-Champaign

Zhiqiang Ma
Intel
==Research Problem==
As the computer industry continues to shift towards multicore processors, concurrent programming and the use of multithreaded designs has increased to keep up with this growing trend. Multithreaded applications can be found in a variety of popular applications today as they take advantage of the multithreaded approach. However, the concepts behind concurrent programming bring with them a host of potential dangers in the form of race conditions and deadlocks resulting from bad programming design and threads accessing shared memory. Fortunately, there are well known and standard methods for dealing with these problems, i.e synchronization primitives. But in real world situations, due to a variety of reasons, as we shall see, programmers often implement their own "ad hoc" synchronizations that eschew common design standards. Ad hoc synchronizations are not well documented and are not discovered by traditional tools for race conditions that look for standard synchronization primitives.

This paper addresses these concerns in two regards, first it details a thorough study of ad hoc synchronizations. It details their nature, dangers, impact on bug detection tools and prevalence in several major open-source applications. Secondly, it introduces SyncFinder, a program that detects all ad hoc synchronizations and automatically annotates the source code where ad hoc sychnronizations are found. This can see use in conjunction with other data race checkers to improve accuracy and to build custom tools for finding deadlocks and bad programming practices.

With detailed analysis of ad hoc synchronization and study of their occurrences in several applications, the research ultimately concludes that they are harmful and should be removed. At the same time, SyncFinder detects and documents ad hoc synchronizations in the source code enabling programmers for the first time to easily track and remove them.

==Background Concepts==
===Race conditions, deadlocks===
Race conditions are an unintended side-effects of programming in concurrent systems, they occur when two or more processes have access to a shared resource and at least one of them have write privilege. This leads to processes modifying the data that all processes share as other may be reading them and results in the reading of stale/incorrect data. They will occur during the execution of the program and often times very difficult to detect or manipulate data in subtle ways.

Deadlock is when two or more processes share a resource and each process is waiting on the other processes to unlock the resource. It becomes a circular chain and no process can continue.

Both these issues occur in concurrent programming and although there are no general solutions for deadlock[[#Foot9|9]], there are suitable methods for dealing with them, and in the case of race conditions, using mutual exclusion locks and synchronization primitives can prevent race conditions. But no programmer is infallible and so there is always the issue of race conditions and deadlocks present in production code.
===Ad Hoc Synchronization===
Ad hoc synchronizations are loops called sync loops that continue until certain conditions are met via outside variables called sync variables. They are designed to control the flow of thread execution much like locking and unlocking of resources. There can be multiple sync variables in a sync loop and they can have multiple exit conditions and dependencies. The diversity of the sync loops, their dependencies and execution paths leads to difficulty in finding them.
===Synchronization primitives===
Synchronization variables act as barriers to memory that prevent threads from accessing the same shared resource concurrently[[#Foot8|8]]. They come in many forms such as mutexes and condition variables.
Mutexes are mutual exclusive locks that threads employ to lock a resource that they need. No other threads can access them at that point. Once they are finished, they release the lock and the other threads can then lock and access the resource.
Condition variables are variables that will block the thread until a certain condition is met. This allows the thread to only execute when it is safe to perform its operation.

==Contribution==

With concurrent programming commonly used in modern applications, we face many issues that result from having simultaneous execution. In order to maintain a concurrent system, synchronizations are required to ensure that the executing tasks do not interfere with each other, which could be disastrous for the system. However, many programmers do not use proper synchronization techniques to deal with these issues. Rather, they implement synchronizations in an ad hoc fashion. In this study, it is shown that ad hoc synchronizations, though implemented as a solution to concurrency issues, are indeed undesirable in a system. This paper details the characteristics of ad hoc synchronizations and the issues associated with this implementation and introduces the program, SyncFinder, which is used to identify such synchronizations in code.

In order to identify the characteristics of ad hoc synchronizations, 12 mainstream programs were examined to find instances of ad hoc synchronizations. These programs were either of server, desktop or scientific type, including Apache, MySQL and Mozilla. Through manual inspection of the source code, these characteristics of ad hoc synchronizations were found.

===Findings===
1.they are prevalent, all applications had them

2. hard to find

3. error prone

4.effect other bug detection

5. They are diverse. Different forms, multiple exits and dependencies

Reasons behind why people use ad hoc synchronization and possible improvements over them ie Synchronization primitives

===SyncFinder===
Intro to what it is and what it does
====How it works====
1. find loops

2. identify sync loops

3. EDV analysis

4. Pruning

5. Annotation of found sync

====Uses====
1. A tool to detect bad practices

2. Extensions to data race detection

====Accuracy====

====Related Work and similar tools====
There has been attempts to remove synchronization issues entirely from concurrent programming, such as transactional memory[[#Foot1|1]], a lock-free synchronization that does not require mutexes, and avoids having to use lock, unlock operations. Other attempts have been made to remove bugs that would otherwise be safe from data races but are are still at risk of unintended effects from thread interactions, such as Atomizer[[#Foot2|2]], a dynamic atomicity checker.

There are tools that detect data races such as CHESS[[#Foot3|3]], a dynamic data race checker that runs through all possible thread execution paths and CTrigger[[#Foot4|4]], a tool that checks for atomicity violations. The problem with these programs is that they only look for standard synchronization methods and structures, such as lock() and cond_wait(). They are not looking for ad hoc synchronizations.

A similar tool to SyncFinder exists that can detect simple spinning, also an ad hoc synchronization[[#Foot5|5]], but it only detects simple spinning and not the more complicated ad hoc variations.

Several studies on bug characteristics[[#Foot6|6]] and concurrency bugs[[#Foot7|7]] have been composed. This paper complements these studies to better understand the nature of ad hoc synchronizations and their occurrence in concurrent programs.

==Critique==
1. Uses static approach, dynamic would be better
* As stated in the paper, dynamic introduces run-time overhead and is not guaranteed to find if not executed in the test cases

2. not entirely accurate, some false positives.

3. In terms of style, lots of unnecessary repetition

==References==
1 M Herlihy and J.E.B. Moss, 2NA0. Transactional Memory:
Architectural Support for Lock-Free Data Structures. [online] Available at: <http://www.cs.brown.edu/~mph/HerlihyM93/herlihy93transactional.pdf> [Accessed 23 November 2010].

2 C Flanagan and S N Freund, 2NA0. Atomizer: A Dynamic Atomicity Checker For Multithreaded Programs (Summary). [online] Company(optional) Available at: <http://www.cs.williams.edu/~freund/papers/atomizer-padtad.pdf> [Accessed 23 November 2010].

3 T Ball,M Musuvathi and S Qadeer, 2NA0. CHESS: A Systematic Testing Tool for Concurrent. [online] Company(optional) Available at: <http://research.microsoft.com/pubs/70509/tr-2007-149.pdf> [Accessed 23 November 2010].

4 Author, 2NA0. Title. [online] Company(optional) Available at: <http://pages.cs.wisc.edu/~shanlu/paper/asplos092-zhou.pdf> [Accessed 23 November 2010].

5 LI, T., LEBECK, A. R., AND SORIN, D. J. Spin detection hardware for improved management of multithreaded systems. IEEE Transactions on Parallel and Distributed Systems PDS-17, 6 (June 2006), 508–521.

6 Author, 2NA0. Title. [online] Company(optional) Available at: <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf> [Accessed 23 November 2010].

7 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf]> [Accessed 23 November 2010].

8 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://www.usenix.org/events/bsdcon/full_papers/baldwin/baldwin_html/node5.html]> [Accessed 23 November 2010].

9 Author, 2010. Title. [online] Company(optional) Available at: <http://homeostasis.scs.carleton.ca/wiki/index.php/Basic_Synchronization_Principles> [Accessed 23 November 2010].

COMP 3000 Essay 2 2010 Question 7

2010-11-27T22:59:00Z

Slay:

==Paper==
===Ad Hoc Synchronization Considered Harmful===
Weiwei Xiong
University of California, San Diego

Soyeon Park, Jiaqi Zhang, Yuanyuan Zhou
University of Illinois at Urbana-Champaign

Zhiqiang Ma
Intel
==Research Problem==
As the computer industry continues to shift towards multicore processors, concurrent programming and the use of multithreaded designs has increased to keep up with this growing trend. Multithreaded applications can be found in a variety of popular applications today as they take advantage of the multithreaded approach. However, the concepts behind concurrent programming bring with them a host of potential dangers in the form of race conditions and deadlocks resulting from bad programming design and threads accessing shared memory. Fortunately, there are well known and standard methods for dealing with these problems, i.e synchronization primitives. But in real world situations, due to a variety of reasons, as we shall see, programmers often implement their own "ad hoc" synchronizations that eschew common design standards. Ad hoc synchronizations are not well documented and are not discovered by traditional tools for race conditions that look for standard synchronization primitives.

This paper addresses these concerns in two regards, first it details a thorough study of ad hoc synchronizations. It details their nature, dangers, impact on bug detection tools and prevalence in several major open-source applications. Secondly, it introduces SyncFinder, a program that detects all ad hoc synchronizations and automatically annotates the source code where ad hoc sychnronizations are found. This can see use in conjunction with other data race checkers to improve accuracy and to build custom tools for finding deadlocks and bad programming practices.

With detailed analysis of ad hoc synchronization and study of their occurrences in several applications, the research ultimately concludes that they are harmful and should be removed. At the same time, SyncFinder detects and documents ad hoc synchronizations in the source code enabling programmers for the first time to easily track and remove them.

==Background Concepts==
===Race conditions, deadlocks===
Race conditions are an unintended side-effects of programming in concurrent systems, they occur when two or more processes have access to a shared resource and at least one of them have write privilege. This leads to processes modifying the data that all processes share as other may be reading them and results in the reading of stale/incorrect data. They will occur during the execution of the program and often times very difficult to detect or manipulate data in subtle ways.

Deadlock is when two or more processes share a resource and each process is waiting on the other processes to unlock the resource. It becomes a circular chain and no process can continue.

Both these issues occur in concurrent programming and although there are no general solutions for deadlock[[#Foot9|9]], there are suitable methods for dealing with them, and in the case of race conditions, using mutual exclusion locks and synchronization primitives can prevent race conditions. But no programmer is infallible and so there is always the issue of race conditions and deadlocks present in production code.
===Ad Hoc Synchronization===
Ad hoc synchronizations are loops called sync loops that continue until certain conditions are met via outside variables called sync variables. They are designed to control the flow of thread execution much like locking and unlocking of resources. There can be multiple sync variables in a sync loop and they can have multiple exit conditions and dependencies. The diversity of the sync loops, their dependencies and execution paths leads to difficulty in finding them.
===Synchronization primitives===
Synchronization variables act as barriers to memory that prevent threads from accessing the same shared resource concurrently[[#Foot8|8]]. They come in many forms such as mutexes and condition variables.
Mutexes are mutual exclusive locks that threads employ to lock a resource that they need. No other threads can access them at that point. Once they are finished, they release the lock and the other threads can then lock and access the resource.
Condition variables are variables that will block the thread until a certain condition is met. This allows the thread to only execute when it is safe to perform its operation.

==Contribution==

With concurrent programming commonly used in modern applications, we face many issues that result from having simultaneous execution. In order to maintain a concurrent system, synchronizations are required to ensure that the executing tasks do not interfere with each other, which could be disastrous for the system. However, many programmers do not use proper synchronization techniques to deal with these issues. Rather, they implement synchronizations in an ad hoc fashion. In this study, it is shown that ad hoc synchronizations, though implemented as a solution to concurrency issues, are indeed undesirable in a system. This paper details the characteristics of ad hoc synchronizations and the issues associated with this implementation and introduces the program, SyncFinder, which is used to identify such synchronizations in code.

===Findings===
1.they are prevalent, all applications had them

2. hard to find

3. error prone

4.effect other bug detection

5. They are diverse. Different forms, multiple exits and dependencies

Reasons behind why people use ad hoc synchronization and possible improvements over them ie Synchronization primitives

===SyncFinder===
Intro to what it is and what it does
====How it works====
1. find loops

2. identify sync loops

3. EDV analysis

4. Pruning

5. Annotation of found sync

====Uses====
1. A tool to detect bad practices

2. Extensions to data race detection

====Accuracy====

====Related Work and similar tools====
There has been attempts to remove synchronization issues entirely from concurrent programming, such as transactional memory[[#Foot1|1]], a lock-free synchronization that does not require mutexes, and avoids having to use lock, unlock operations. Other attempts have been made to remove bugs that would otherwise be safe from data races but are are still at risk of unintended effects from thread interactions, such as Atomizer[[#Foot2|2]], a dynamic atomicity checker.

There are tools that detect data races such as CHESS[[#Foot3|3]], a dynamic data race checker that runs through all possible thread execution paths and CTrigger[[#Foot4|4]], a tool that checks for atomicity violations. The problem with these programs is that they only look for standard synchronization methods and structures, such as lock() and cond_wait(). They are not looking for ad hoc synchronizations.

A similar tool to SyncFinder exists that can detect simple spinning, also an ad hoc synchronization[[#Foot5|5]], but it only detects simple spinning and not the more complicated ad hoc variations.

Several studies on bug characteristics[[#Foot6|6]] and concurrency bugs[[#Foot7|7]] have been composed. This paper complements these studies to better understand the nature of ad hoc synchronizations and their occurrence in concurrent programs.

==Critique==
1. Uses static approach, dynamic would be better
* As stated in the paper, dynamic introduces run-time overhead and is not guaranteed to find if not executed in the test cases

2. not entirely accurate, some false positives.

3. In terms of style, lots of unnecessary repetition

==References==
1 M Herlihy and J.E.B. Moss, 2NA0. Transactional Memory:
Architectural Support for Lock-Free Data Structures. [online] Available at: <http://www.cs.brown.edu/~mph/HerlihyM93/herlihy93transactional.pdf> [Accessed 23 November 2010].

2 C Flanagan and S N Freund, 2NA0. Atomizer: A Dynamic Atomicity Checker For Multithreaded Programs (Summary). [online] Company(optional) Available at: <http://www.cs.williams.edu/~freund/papers/atomizer-padtad.pdf> [Accessed 23 November 2010].

3 T Ball,M Musuvathi and S Qadeer, 2NA0. CHESS: A Systematic Testing Tool for Concurrent. [online] Company(optional) Available at: <http://research.microsoft.com/pubs/70509/tr-2007-149.pdf> [Accessed 23 November 2010].

4 Author, 2NA0. Title. [online] Company(optional) Available at: <http://pages.cs.wisc.edu/~shanlu/paper/asplos092-zhou.pdf> [Accessed 23 November 2010].

5 LI, T., LEBECK, A. R., AND SORIN, D. J. Spin detection hardware for improved management of multithreaded systems. IEEE Transactions on Parallel and Distributed Systems PDS-17, 6 (June 2006), 508–521.

6 Author, 2NA0. Title. [online] Company(optional) Available at: <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf> [Accessed 23 November 2010].

7 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.1203&rep=rep1&type=pdf]> [Accessed 23 November 2010].

8 Author, 2NA0. Title. [online] Company(optional) Available at: <[http://www.usenix.org/events/bsdcon/full_papers/baldwin/baldwin_html/node5.html]> [Accessed 23 November 2010].

9 Author, 2010. Title. [online] Company(optional) Available at: <http://homeostasis.scs.carleton.ca/wiki/index.php/Basic_Synchronization_Principles> [Accessed 23 November 2010].

Talk:COMP 3000 Essay 2 2010 Question 7

2010-11-26T00:15:06Z

Slay:

Talk:COMP 3000 Essay 2 2010 Question 7

2010-11-26T00:14:57Z

Slay:

'''Attendence. Please mark your name to say you're here'''

Stephany Lay --[[User:Slay|Slay]] 19:45, 15 November 2010 (UTC)

--[[User:Asoknack|Asoknack]] 16:00, 15 November 2010 (UTC)

--[[User:Smcilroy|Smcilroy]] 18:43, 15 November 2010 (UTC)

Lester Mundt
--[[User:Lmundt|Lmundt]] 18:58, 15 November 2010 (UTC)

Thomas McMahon
--[[User:cha0s|cha0s]]

Martin Kugler
--[[User:Mkugler|Mkugler]] 02:42, 18 November 2010 (UTC)

So only 2 days left before it's due! I'd like to hear what others are planning on contributing and when, since only myself and Slay have done any work on the actual essay. It would be nice to hear from you guys, even if its to say that your busy and are going to work on it on Thursday etc. etc.--[[User:Smcilroy|Smcilroy]] 22:05, 23 November 2010 (UTC)

So, what's the plan for this? How do we want to do this? Given the duedate looming in 4 days we should probably get talking about it. What are your thoughts?
--[[User:Mkugler|Mkugler]] 23:00, 21 November 2010 (UTC)
::Hey! So I added an intro and it covers the research problem to. I also added a bare bones skeleton of what we'll probably end up talking about. Personally, I think people should choose a couple of subsections and sections that they will work on and just put your name beside it. It seems to work best as people then have a sense of ownership and responsibility to that particular topic and aren't overwhelmed at editing the entire essay, at least for the beginning. That doesn't mean we can't all edit each others work though! I welcome any changes to the intro. Anyways, that's my 2 cents. --[[User:Smcilroy|Smcilroy]] 06:06, 22 November 2010 (UTC)
::As critique is our own opinion, we should discuss our thoughts. Having only one person writing that would not express everyone's opinions. --[[User:Slay|Slay]] 20:48, 22 November 2010 (UTC)

Hey, gonna be fleshing out the Contribution section, probably the stuff under the SyncFinder heading. Just wanted to give people a head's up so we don't waste time all doing the same thing.
--[[User:Mkugler|Mkugler]] 03:09, 24 November 2010 (UTC)
I will do the Findings section for now then. I'm unsure when I'll get to it though. I'll try for this weekend. --[[User:Slay|Slay]] 00:14, 26 November 2010 (UTC)

Talk:COMP 3000 Essay 2 2010 Question 7

2010-11-22T20:48:09Z

Slay:

COMP 3000 Essay 2 2010 Question 7

2010-11-22T20:44:29Z

Slay: /* Critique */

Talk:COMP 3000 Essay 2 2010 Question 7

2010-11-16T15:11:14Z

Slay:

Talk:COMP 3000 Essay 2 2010 Question 7

2010-11-15T19:45:21Z

Slay:

COMP 3000 Essay 2 2010 Question 7

2010-11-14T19:41:13Z

Slay: Created page with " ---- See discussion"

----
See discussion

Talk:COMP 3000 Essay 2 2010 Question 7

2010-11-14T15:46:13Z

Slay: Created page with "'''Attendence. Please mark your name to say you're here''' Stephany Lay"

'''Attendence. Please mark your name to say you're here'''

Stephany Lay

Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-14T16:02:10Z

Slay: /* three approaches */

== Microkernel ==
* Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
* Keep basic functionality in kernel to handle sharing of resources
* Separation allows for manageability and security, corruption in one does not necessarily cause failure in system
* Large amount of moving from a process to Kernel to user space and back again, this is a costly operation.

----

''' Microkernel '''
* try's to minimize the amount of software that is mandatory or required [7]
advantages of Microkernel
* favors a modular system structure [7]
* one failure of a program does not impact any other programs [7]
* can support more than one api or strategies since all programs are separated [7]
==== Microkernel Concepts ====
* piece of code is allowed in the kernel only if moving it outside the kernel would adversely affect the system. [7]
* any subsystem program created must be independent of all other subsystem's, any subsystem that is used can guarantee this from all other subsystems [7]
===== Address Space =====
* a mapping that relates the physical page to the virtual page. [7]
* processor specific [7]
* hide's the hardware's concept of address space [7]
* based off the idea of recursion each subsystem has it's own address space [7]
* the micro kernel provides 3 operations [7]
** Grant [7]
*** allows the owner to give a page to a recipient, provided the recipient want's it the page is removed from the owner's address space and but in the recipients. [7]
*** must be available to the owner. [7]
** Map [7]
*** allows the user to share a page with a recipient [7]
*** page is not removed from the owner's address space. [7]
** Flush [7]
*** remove's the page from all recipients address space [7]
*** how does this work with Grant --[[User:Asoknack|Asoknack]] 19:10, 12 October 2010 (UTC)
* allows memory management and paging out side the kernel
* Map and flush is required for memory manger's and pagers [7]
* can be used to implement access right's [7]
* controlling I/O Right's and driver's are not done at kernel level [7]

===== Thread's IPC =====
* Threads
** in the kernel [7]
** Since a thread has an address space , all changes to the thread need to be done by the kernel [7]
* IPC [7]
** in the kernel IPC
** grant and map also need IPC (So buye the priciple above this has to be in the kernel)[7]
** basic way for sub process to communicate. [7]
* Interrupts
** partially in the kernel [7]
** hard ware is a set of thread's which are empty except for there unique sender id [7]
** transformation of the message to the interrupt is done in the kernel [7]
** the kernel is not involved in device - specific interrupt's and does not understand the interrupt. [7]
*** resting the interrupt is done at user level [7]
** if a privileged command is need it is done implicitly the next time an IPC command is sent from the device [7]

===== Unique Identifiers =====

== Virtual Machine ==
* Partitioning or virtualizing resources among OS virtualization running on top of host OS
* Virtualized OS believe running on full machine on its own

----
System Level Virtualization

=== VMM ===
* stands for Virtual Machine Monitor, also known as the hyper-visor[4]
* responsible for virtualization of hardware(mapping physical to virtual) and the VM that run on top of the virtuallized hardware [4]
* usually a small os with no drivers , so it is coupled with a linux distro that provides device / hardware access [4]
** the os that the VMM is using for driver's is called the hostOS [6]
*the hostOS provides login and physical access to the hardware as well as management for the VMM [6]
=== VM ===
* the OS that the vm is running is called the guestOS [6]
* the guestOS only sees resources that have been allocated to the VM [6]
==== three approaches ====
*Type I virtualization [5]
** runs off the physical hardware [4]
** Isolation of the guestOs from the hardware is done threw processe level protection meachnism[6]
*** ring 0 = VMM [6]
*** ring 1 = VM [6]
*** this means all instructions from the VM must go threw the VMM [6]
** since there can be multiple VM's on a computer the scheduling is done by the VMM [6]
** on boot the VMM creates a hardware platform for the VM [6]
** load's the VM kernel into virtual memory and then boot's it like a regular computer [6]
** ex. Xen [4]
*Type II virtualization [5]
** run off the host Os [4]
** ex. VMware , QEMU [4]
* Para-virtualization [6]
** Similar to Type but use the HostOs for Device driver access [6]
** Provide a virtualization that is similar to hardware [From the paper posted, no citation yet]
** GuestOS and Hypervisor work together to improve performance

----
==== ====
(Not complete but most of article 9)
Classical Virtualization
* VMMs allow programs in virtual environments to run natively other than resource usage
** Dominant instructions executed directly on cpu
** vmm completely controls system resources
** often need to emulate every native instruction which would severely effect the performance
** sensitive instruction that violate safety and encapsulation
** vmm handles them as priviledged instructions

x86 Virtualization
* virtualization in personal work stations rather than mainframes
** rings that allow isolation between virtual machines
** most privileged in ring 0 and least in ring 3. The operating system runs in ring 0 and user apps in ring 3
*** vmm in ring 0 and vms in lesser privilege rings (1 or 3)
*** guestOS believes its in ring 0
* address space compression, where to run the VMM
** if run using guest address space, guest can find out its virtualized or compromise the isolation
* does not trap all sensitive instructions but can handle them, violates classical virtualization description
* some privileged access fail without faulting
* interrupt virtualization - VMM handles AND guestOS handles
* binary translation - improve performance
* rewriting instructions and trapping before problems arrise

Paravirtualization
* guestOS become exposed to vm information so that the guest is aware that it is virtualized and can make decisions based on this
* allows to avoid problem instructions
* Xen
* guestOS must be modified and is not natively running
**works with the hostOS to run efficiently

VMM types
* hostedVMM - executes in hostOS and uses the drivers and support of the OS
* Stand-aloneVMM - runs directly on hardware and uses it's own drivers and services
* hybridVMM - runs a serviceOS where requests to hardware go through (I/O)

Device Emulation
* implement real hardware in software
* completely virtual device that the guest interacts with
* mapped to physical hardware that handles the interactions but the emulation allows conversion
* allows the vm to be easily migrated between machines as it does not rely on the physical hardware
* allows having multiple vms and simplifies sharing (multiplexing)
* poor performance as the vmm needs to do a lot to virtulize the machine

Paravirtualization
* modified guestOS to cooperate with VMM
* VMM does not have to do everything to handle device drivers
* not everything can be paravirtualized
* proprietary os and device drivers can't be paravirtualized
* still allows an increase in performance
* eventing or callback mechanism
** guestOS modifies interrupt mechs
* modifications are not applicable to all guestOS

Dedicated Devices
* does not virtualize device but assigns directly to guest vm
* uses guest's drivers instead of host
* simplifiest vmm by removing handing of i/o securily
* limited physical devices that can be dedicated
* dificult to migrate vm as it depends on the pairing with this resource
* elims over-head of virtualization and simplicity in vmm
* direct memory access not supported

== Exokernel ==
* Micro-kernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
* Less functionality provided by kernel, security and handling of resource sharing
* Once application receives resource, it can use it as it wishes/in control
* Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware

----
* multiplex resources securely providing protection to mutual distrustful application threw the use of secure binding's[1]
* Goal of the exokernel is to give LibOS maximum freedom with out allowing them to interfere with each other. to do this the exokernel separates protection from management in doing this it provide 3 important tasks[1]
** tracking ownership of resources [1]
** ensuring protection by guarding all resource usage and binding points (not to shure what binding points are)[1]
** revoking access to the resources [1]
* LibrayOS (LibOs)
** Reduces the number of kernel crossings[1]
** Not trusted by the exokernel so can be trusted by the application , Example given is a bad parameter passed to the LibOs only the application is affected.[1] (So LibOs cant interact with kernel ???)
** Any application running on the Exokernel can change the LibrayOs freely [1]
** Application that use LibOS that implement standard interfaces (POSIX) will be portable on any system with the same interface [1]
** LibOs can be made portable if it is designed to interact with a low-level machine independent level to hide hardware details [1]

=== Exokernel Design ===
==== Design Principles ====
*Securely Expose Hardware [1]
** an Exokernel tries to create low level primitives that the hardware resources can be accessed from, this also includes interrupts,exceptions [1]
** the exokernel also export privileged instructions to the LibOS so that traditional OS abstractions can be implemented (eg Process , address pace)[1]
** Exokernels should avoid resource management except when required protection ( allocation , revocation , ownership)[1]
** application based resource management is the best way to build flexible efficient flexible systems [1]
*Expose allocation[1]
** allow LibOs to request physical resources [1]
** resource allocation should not be automatic, the LibOS should participate in every single allocation decision [1]
*Expose Names[1]
** Use physical name's when ever possible[3] (not to sure what physical names are, I think it is as simple as what the hardware is called)--[[User:Asoknack|Asoknack]] 20:27, 9 October 2010 (UTC)
** Physical names capture useful information [3]
*** safer than and less resource intensive than virtual names as no translations are needed[3]
*Expose Revocation [1]
** use visible revocation protocol [1]
** allows well behaved LibOS to preform application level resource management [1]
** Visible revocation allows the LibOS to choose what instance of the resource to release[1](Visible means that when revocation happens the exokernel tell the LibOS that resource is being revoked)
''' Policy '''
* LibOS handle resource policy decisions
* Exokernels have a policy to decided between competing LibOS (Priority , share of resources)
** it enforces this threw allocation and deallocation (every thing can achieved threw this even what block to write and such)

==== Secure Bindings ====
* Used by the exokernel to allow the LibOS to bind to resources [1]
* Allows the separation of protection and resource use [1]
* only checks authorization during bind time [1]
** Application's with complex needs for resources only authorized during bind.[1]
* access checking is done during access time and there is no need to understand complex resources needs during access[1]
** (this means that the exokernel checks once to make sure an application has authorization once approved, when the application tries to use the resource the exokernel is only concerned about policy conflict's)--[[User:Asoknack|Asoknack]] 18:20, 9 October 2010 (UTC)
** allows the kernel to protect the resources with out understanding what the resource is [1]
*three way's to implement
* Hardware Mechanisms [1]
* Software caching [1]
* Downloading application code [1]
''' Downloading Code to the Kernel '''
* used to implement secure bindings , and improve performance[1]
** eliminate the number of kernel crossings [1]
** downloaded code can be run with out the application to be scheduled [2]
==== Visible Resource Revocation ====
* Used for most resources [1]
** allows for LibOS to help with deallocation [1]
** LibOS are able to garner what resources are scare [1]
* Slower than Invisible as application involvement is required [1]
** ex of when invisible is used is Processor addressing-context identifiers [1]
==== Abort Protocol ====
* allows the exokernel to take resources away from the LibOS [1]
* used when the LibOS fails to respond to the revocation request [1]
* Exokernel must be careful not to delete as the LibOS might need to write some system critical data to the resource [1]

== Comparisons ==
====Exokernel/Microkernel====
'''Similarities'''
* Limited functionality in kernel
** functionality in kernel to handle sharing of resources and security
** avoids programming directly to hardware which creates a dependency
* Additional functionality provided in user space as processes
'''Differences'''
* Minimal abstractions provided by the kernel
** Applications given more power in exokernel

====Exokernel/VM====
'''Similarities'''
* Idea of partitioning resources between applications/OSs
* "Control" of resource given
* Isolation from other applications/OSs
'''Differences'''
* Exokernel runs applications, VM runs OS
* VM uses a hostOS and guestOSs run on top
* Virtualization on VMs, Exokernel deals with real resources
* VM hides a lot of information because it emulates. Exokernel does not.

====Microkernel/VM====
'''Differences'''
* With a virtual machine, you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System.
* This can be costly but the benefits are that it's easier and all the standard OS features are available.

== References ==
[1]<nowiki> Engler, D. R., Kaashoek, M. F., and O'Toole, J. 1995. Exokernel: an operating system architecture for application-level resource management. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 251-266. DOI= http://doi.acm.org/10.1145/224056.224076 </nowiki>

[2]<nowiki>Engler, Dawson R. "The Exokernel Operating System Architecture." Diss. Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998. Web. 9 Oct. 2010. <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.61.5054&rep=rep1&type=pdf>.</nowiki>

[3]<nowiki>Kaashoek, M. F., Engler, D. R., Ganger, G. R., Briceño, H. M., Hunt, R., Mazières, D., Pinckney, T., Grimm, R., Jannotti, J., and Mackenzie, K. 1997. Application performance and flexibility on exokernel systems. In Proceedings of the Sixteenth ACM Symposium on Operating Systems Principles (Saint Malo, France, October 05 - 08, 1997). W. M. Waite, Ed. SOSP '97. ACM, New York, NY, 52-65. DOI= http://doi.acm.org/10.1145/268998.266644 </nowiki>

[4]<nowiki>Vallee, G.; Naughton, T.; Engelmann, C.; Hong Ong; Scott, S.L.; , "System-Level Virtualization for High Performance Computing," Parallel, Distributed and Network-Based Processing, 2008. PDP 2008. 16th Euromicro Conference on , vol., no., pp.636-643, 13-15 Feb. 2008
DOI= http://doi.acm.org/10.1109/PDP.2008.85 </nowiki>

[5]<nowiki>Goldberg, R. P. 1973. Architecture of virtual machines. In Proceedings of the Workshop on Virtual Computer Systems (Cambridge, Massachusetts, United States, March 26 - 27, 1973). ACM, New York, NY, 74-112. DOI= http://doi.acm.org/10.1145/800122.803950 </nowiki>

[6]<nowiki>Vallee, G., Naughton, T., and Scott, S. L. 2007. System management software for virtual environments. In Proceedings of the 4th international Conference on Computing Frontiers (Ischia, Italy, May 07 - 09, 2007). CF '07. ACM, New York, NY, 153-160. DOI= http://doi.acm.org/10.1145/1242531.1242555 </nowiki>

[7]<nowiki>Liedtke, J. 1995. On micro-kernel construction. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 237-250. DOI= http://doi.acm.org/10.1145/224056.224075 </nowiki>

[8]<nowiki>Microkernel verses monolithic kernel
http://www.vmars.tuwien.ac.at/courses/akti12/journal/04ss/article_04ss_Roch.pdf - Roch</nowiki>

I will site it/reference it better later

[9]Fisher-Ogden J. 2006. Hardware Support for Efficient Virtualization. University of California, San Diego. http://cseweb.ucsd.edu/~jfisherogden/hardwareVirt.pdf

Not completely sure of the citation style used above.

== Unsorted ==
An overview of exokernels,virtual machines, microkernels *[http://www2.supchurch.org:10999/files/school/classes/CSCI4730/Lectures/grad-structures.ppt Overview](Power Point) 
Should not be used as a source but an overview.

The original paper on [http://portal.acm.org/citation.cfm?id=224076 Exokernels] --[[User:Gautam|Gautam]] 22:39, 6 October 2010 (UTC)

Exokernel-
Minimalistic abstractions for developers
Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs.
Exokernel – fewest hardware abstractions to developer
Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system
Virtual machine is a simulation of any or devices requested by an application program
Exokenel – I’ve got a sound card
Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match
Microkernel – I’ve got sound card that plays Khazikstan sound format only
MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below
-Rovic

Outlining some main features here as I see them.

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have.

I'll locate some references later on. --[[User:Slay|Slay]] 15:00, 7 October 2010 (UTC)

I'm just going to post my answer for question 1 on the individuel assignment and hope it helps. --[[User:Aellebla|Aellebla]] 15:06, 12 October 2010 (UTC)

The design of the micro kernel was to take everything they could out of the Kernel and put it into a process. For ex, networking would be put into a process instead of staying in the kernel. The micro kernel dev's tried to keep lots of things in user space for efficiency. But one major problem with this is there would be a large amount of moving from a process to the kernel to user space and back again and this is a costly, non efficient process.It was an application specific OS, there was no multiplexing. With a virtual machine you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System. This is very heavy however but the benefits are that it‟s easy and all the standard OS features are there whereas in a microkernel setup they would not all be there and this can be seen as a compromise.

Exokernels can be seen as a compromise to virtual machines and microkernels because virtual machines emulate and exokernels do not. When you emulate something you hide a lot of the actual information because you wouldn‟t be able to see the „real‟ hardware. If we look at a virtual box setup running Linux, and we go look at all the hardware, it will be displayed as fake hardware.

Maybe we can have an introduction - paragraph or so on each type - then similarities - differences - and the compromise. I am going to do some research and writing this weekend and I will put some up -- Jslonosky

btw in my page (i guess you can call it that) i have some resources i have found --[[User:Asoknack|Asoknack]] 15:50, 8 October 2010 (UTC)
- Wow, nice man. I will go ahead and write up the descriptive paragraphs on each kernel and virtual machine if no one minds. --Jslonosky

I think we should divide up the paragraphs and proofread each others instead. (Are there only 4 of us?) I don't have much time to work on this today though but I'll try to work on it tomorrow morning. - Slay

Sure guy. That sounds good. There should be 5 or 6 of us though.. . Oh well. Their loss. I will do some before or after work today. Ill start with Microkernel since there is not a large amount of info here, and so we don't overlap each other - JSlonosky

yeah i think there was more like 7 of us btw if any one has any more information feel free to add it would be nice if you add the references so that way citing is really easy on acm.org it will auto give you the citation info (where it says Display Formats click on ACM Ref and new window with the citation info auto pop's up) --[[User:Asoknack|Asoknack]] 02:28, 11 October 2010 (UTC)

I added an outline of the similarities and differences. Add any more that I missed. These are from observations so I don't have any resources. -Slay
That's probably fine. Our textbook probably outlines some of them, so I am sure we can find a few there - JSlonosky

Talked to the teacher today and for VM he said we should focus on the implementation such as Xen and VMware , he also said to talk about para virtualization --[[User:Asoknack|Asoknack]] 18:42, 12 October 2010 (UTC)

A paper about emulation and paravirtualization [http://portal.acm.org/citation.cfm?id=1189289&coll=GUIDE&dl=GUIDE&CFID=105648137&CFTOKEN=47153176&ret=1#Fulltext link] - Slay

Oh no big words. Sorry about the Microkernels not done yet. Working on an outline now. Finally found how to access the ACM through carleton. Gawd.
I am planning an outline, quick bit about kernels in general, (maybe mention monolith kernels?), and what microkernels do.
I see the microkernel outline info and a reference ( Whomever did that == hero: true) about the scheduling and the Memory management. Should that be included in kernels in general and then mention what microkernels build upon/change? - JSlonosky

Sorry late to the party here. My mistake was not checking the discussion page when I checked in. I don't want to trample anyone's current work but I don't see any work on the final essay done. I would love to help just need to know where I can step in so as to not screw anyone else up. -- [[User:Cling|Cling]]

I don't think I'll be able to write up something for the final essay, even though I suggested splitting it. I'll do research tonight though on the paravirtualization. If I find the time, I'll try to write something. Sorry about that. --[[User:Slay|Slay]] 21:52, 13 October 2010 (UTC)

We all have 3004 to do too, man. I do not think anyone has chosen to do Virtual Machine section yet, or the Exokernel itself. But the contrast paragraph and the intro is chosen, and intro is done. Microkernel and kernel will be done in a hour I hope. -- JSlonosky

I can attempt to write up anything, the issue is I don't have any context on what to write, how do I tie it in to the rest of the essay? I only have a Japanese Quiz tomorrow morning then I should be good to write anything up for the rest of the day. As someone who has already written part of the essay, and assuming I attempt the exokernel section, how much do you think I should write? Should it just be about exokernel or should there be comparisons to the other topics? Thanks --[[User:Cling|Cling]] 23:14, 13 October 2010 (UTC)

Go with the Exokernel itself. Slade is getting off work in a hour and we can double check what he is doing then. We can put it together tomorrow sometime, and fill in the other stuff. - JSLonosky

I'll attempt to work on VM tonight, then. I would feel so bad if I didn't write anything. -Slay

Still wondering how much to write, I think we should decide on a decent word count or length so we don't have one short section (which would probably be mine) and/or one massive section that dwarfs all the others. If anyone has already written a section could you post your word count so we can aim to be around there, it would obviously be just a recommendation but it's just better to be on the safe side and have everything uniform. I haven't seen any formal requirements for the essay but I could be wrong, I also haven't been to class in a while. --[[User:Cling|Cling]] 23:33, 13 October 2010 (UTC)

Yeah Slay, VM probably doesnt have much to write about. Get something down, and we can go over it. CLing, Just write what you think. There is not a lot to go over if I write kernel/microkernel well enough. What is a exokernel? exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction, basically (As said by Slade). I will probably end up with 500 or a bit more words. -- JSlonosky

Sound off!

Who's actually reading this? Add your name to the list...

Rovic P.
Jon Slonosky
Corey Ling
Steph Lay
Aaron .L

== The Essay ==

Let's actually breakdown the essay into components then write it here.

I'd like to go along the premise that microkernels and and virtual machines are "weaker" than exokernels in design for the essay. If anyone has any objections, add it here.

-Slade

what do you mean by "weaker"(i think you mean exokernels' takes the best of both worlds ) --[[User:Asoknack|Asoknack]] 02:45, 13 October 2010 (UTC)

What I mean by weaker is that we should focus on the things microkernels and virtual machines may not do as well compared to a system based off an exokernel design and then focus on how an exokenenel can take the best of both worlds. Please choose which section you will work on, that's not to say it'll be the only part you do, but rather we'll all contribute to each part please. 1 day left.
-Slade

...to the extent that exokernels be seen as a compromise between virtual machines and microkernels.
-I'll work on the initial intro. -Slade

3 paragraphs that prove it
Explain how the key design characteristics of these three system architectures compare with each other.

intro/thesis statement -Rovic P.

In Computer Science, the kernel is the component at the center of the majority of operating systems. The kernel is a bridge for applications to access the hardware level. It is responsible for managing the system's resources such as memory, disk storage, task management and networking. We are comparing Exokernels to Microkernels and Virtual Machines by looking at how the kernel goes about such management and its connections. In the Exokernel conceptual model, we can see exokernels become much smaller than microkernels because as this design shows, they are tiny and strive to keep functionality limited to protection and multiplexing of resources. The Virtual Machine Implementation of virtualizing all devices on the system may provide compatibility, but it also adds a layer of complexity within the system. This is less efficient than a real machine as it accesses the hardware indirectly. It can be observed by examining how the exokernel provides low level hardware access and provides custom abstraction to those devices. This is done in order to improve program performance as opposed to a VM's implementation. The exokernel concept has a design that can take the better concepts of microkernels and virtual machines to the extent that exokernels can be seen as a compromise between a virtual machine and a microkernel.

Paragraph 1 -Microkernel -Jon S.

The kernel is the most important part of an operating system. An operating system could not function without the kernel.

A kernel is the lowest level section of an operating system. Within a system, it has the most privileges. It runs along side of the ‘user space’. It is in the ‘user space’ where a user has access. This is also where the user can run its applications and libraries.[8] This leaves the kernel with the need to manage the other necessary processes. For example, the kernel could manage the File Systems and complete process scheduling. The kernel is layered with the most authoritative process on its lowest level.[8] A monolithic kernel, which is a kernel that contains all mandatory processes within itself, was the common kernel type of the earlier versions of today’s operating systems utilized. However, this architecture had problems. [8] If the kernel needed to be updated with more code, or a change in the system, the entire kernel would need to be compiled. Therefore, due to the amount of processes within it, it would take an inefficient amount of time. Here, a microkernel becomes practical.

The concept of a microkernel, is to reduce the code within the kernel. The microkernel is only included in the kernel if it would impact the system. There are a variety of ways the system could be affected if a microkernel were to be implemented, for example, there would be increased performance and efficiency. [7] So, a microkernel is a kernel that has a reduced amount of mandatory software within itself. This means that it contains less software that it has to manage, and has a reduced size. A microkernel that emerged at the end of the 1980’s to the early 1990’s has the structure that processes like the File Systems and the Drivers are removed from it, leaving the kernel with process control and input/out control, and interrupts. [8] This new structure makes the system much more modular, and easier to provide solutions. If a driver must be patched or upgraded, the kernel does not need to be recompiled. [7] The old driver can be removed, and while the device waits for the system to recognize it, the operating system replaces the driver. This lets real-time updating, and it can be done while the computer is still functional. This can reduce the complete crash of the system. If a device fails, the kernel will not crash itself, like a monolithic kernel would. The microkernel can reload the driver of the device that failed and continue functioning. [7]

Want more on the scheduling? I can do that if wanted. -key note on exokernel's mutiplexing vs microkernel's messaging, exo more efficient so perhaps running with the idea that messaging b/w processes not necessarily the ideal way need to also start outlaying weaknesses in the design as well in order to play up the idea that an exokernel just does it better -Slade

Paragraph 2 -Virtual Machine -Steph L.

A Virtual Machine, or VM, is a software abstraction of a physical machine. This entails virtualization of the physical machines resources in order to share them among OS run in the VM. Virtualizing these resources allow the OS to run as if it were on a full machine when, in reality, it is actually running in a virtualized environment on top of a hostOS, the OS actually running on the machine, sharing the resources.

Virtual Machines generally contain two key components, the Virtual Machine Monitor, or VMM and the VM.

The VMM, also known as the hypervisor, manages the virtualization of the physical resources and the interactions with the VM running on top. [4] In other words, it mediates between the virtualized world and the physical world, keeping them separate and monitoring their interactions with each other. The hypervisor is what allows the VM to operate as if it were on its own machine by handling any requests to resources and maintaining these requests with what has actually been provided to the VM by the hostOS. The hostOS provides management for the VMM as well as allowing physical access to devices, hardware and drivers. [6]

The VM is what contains the OS we are running through virtualization. [6] This OS is called the guestOS and it will only be able to access any resources that have been made available to the VM by the hostOS. [6] Otherwise, the guestOS will not know about any other resources and does not have direct access to physical hardware. This will be taken care of by the VMM but the guestOS will execute as its own machine, unaware of this mediator.

There are various ways of implementing hardware virtualization in a system to allow VMs to run. This includes device emulation, paravirtualization and dedicated devices. [9]

In device emulation, the VMM provides a complete virtualization of a device for the guestOS to interact with, in software. [9] The VMM will map this virtualized device to the physical resource and handle any interactions between them. This will usually include converting instructions from the guestOS into instructions that are compatible with the device. [9] Device emulation allows for the VM to be migrated easily to another machine as it is not dependent on the physical devices but on the software emulations instead. [9] It also allows for simpler multiplexing between multiple virtual machines as it can handle sharing though these virtualized devices. [9] A drawback of emulation, however, is poor performance as the VMM must handle every request and convert them to be compatible with the physical device. [9] However, despite its poor performance, emulation is the most common form of virtualization.

Paravirtualization allows for a boost in performance by having the guestOS and the hostOS work together to improve performance. [9] In paravirtualization, the guestOS is not a native OS and must be modified so that it is aware that it is a virtualized system. [9] As the guestOS is aware of this, it can now make better decisions about how it accesses devices. As the guestOS will be able to handle its decisions better, the VMM’s responsibility is reduced as it now does not have to translate between the guestOS and the physical devices. [9] Though the performance boost is a great advantage, there are many disadvantages to this. You can only use paravirtualization if you can implement the modifications to the guestOS. Not everything can be paravirtualized and as such, this limits the cases in which this method can be used. [9] Also, every guestOS must be modified in order to be used in paravirtualization. The modifications will differ in various OS and so, there is also the task of implementing these changes to make a guestOS compatible. [9]

Instead of virtualizing the hardware and mediating between with the VMM, dedicated devices allow mapping directly to the guestOS. [9] In this method, the device will use the guestOS’s drivers instead of the hostOS’s. [9] Using this method allows the guestOS to use the hardware to its full extent without having to deal with the VMM. This simplifies the VMM by eliminating the overhead in virtualizating the hardware and handling the requests to devices. [9] However, there are limited physical resources to be dedicated to a guestOS and this also makes migration difficult as the guestOS is dependent on the physical device. [9]

'''notes'''
- it ended up being quite lengthy. I mainly focused on the device virtualization rather than the architecture of a VM (like x86 virtualization). I'll put up my notes for the paper I found for virtualization. I didn't talk about Xen or VMware though. If any of that is needed, I can try to continue working on it tonight but I have another priority.

-try focusing on the emulation side of VM where emulation's weaknesses vs direct hardware access or custom abstraction that exokernels -Slade

Paragraph 3 -Exokernel -Corey L

Paragraph 4 - Contrast/Compromise --[[User:Asoknack|Asoknack]]

Conclusion - Jon S. - Only a sentence per paragraph, excluding Intro

Sweet. Looks like we got it covered. We should read each others parts and put suggestions and edits. One of us should try and change it to one style if there are contradictions. And to put it on the main page. We can figure that out tomorrow. - Jon S

Once the other parts are up and you see anything you know of as a good reference to back it up, put the link so we can use it. -Slade

I made some edits to the first two paragraphs. I just reworded some of the unclear sentences and some grammatical errors. I'll work on editing more of it after comp 3007. Also when all the parts are up i can go through it and link the paragraphs together so it can be read more like an essay --[[User:Aellebla|Aellebla]] 15:18, 14 October 2010 (UTC)

==Potential Test Questions==

Add potential test questions here:

Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-14T16:01:12Z

Slay: /* three approaches */

== Microkernel ==
* Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
* Keep basic functionality in kernel to handle sharing of resources
* Separation allows for manageability and security, corruption in one does not necessarily cause failure in system
* Large amount of moving from a process to Kernel to user space and back again, this is a costly operation.

----

''' Microkernel '''
* try's to minimize the amount of software that is mandatory or required [7]
advantages of Microkernel
* favors a modular system structure [7]
* one failure of a program does not impact any other programs [7]
* can support more than one api or strategies since all programs are separated [7]
==== Microkernel Concepts ====
* piece of code is allowed in the kernel only if moving it outside the kernel would adversely affect the system. [7]
* any subsystem program created must be independent of all other subsystem's, any subsystem that is used can guarantee this from all other subsystems [7]
===== Address Space =====
* a mapping that relates the physical page to the virtual page. [7]
* processor specific [7]
* hide's the hardware's concept of address space [7]
* based off the idea of recursion each subsystem has it's own address space [7]
* the micro kernel provides 3 operations [7]
** Grant [7]
*** allows the owner to give a page to a recipient, provided the recipient want's it the page is removed from the owner's address space and but in the recipients. [7]
*** must be available to the owner. [7]
** Map [7]
*** allows the user to share a page with a recipient [7]
*** page is not removed from the owner's address space. [7]
** Flush [7]
*** remove's the page from all recipients address space [7]
*** how does this work with Grant --[[User:Asoknack|Asoknack]] 19:10, 12 October 2010 (UTC)
* allows memory management and paging out side the kernel
* Map and flush is required for memory manger's and pagers [7]
* can be used to implement access right's [7]
* controlling I/O Right's and driver's are not done at kernel level [7]

===== Thread's IPC =====
* Threads
** in the kernel [7]
** Since a thread has an address space , all changes to the thread need to be done by the kernel [7]
* IPC [7]
** in the kernel IPC
** grant and map also need IPC (So buye the priciple above this has to be in the kernel)[7]
** basic way for sub process to communicate. [7]
* Interrupts
** partially in the kernel [7]
** hard ware is a set of thread's which are empty except for there unique sender id [7]
** transformation of the message to the interrupt is done in the kernel [7]
** the kernel is not involved in device - specific interrupt's and does not understand the interrupt. [7]
*** resting the interrupt is done at user level [7]
** if a privileged command is need it is done implicitly the next time an IPC command is sent from the device [7]

===== Unique Identifiers =====

== Virtual Machine ==
* Partitioning or virtualizing resources among OS virtualization running on top of host OS
* Virtualized OS believe running on full machine on its own

----
System Level Virtualization

=== VMM ===
* stands for Virtual Machine Monitor, also known as the hyper-visor[4]
* responsible for virtualization of hardware(mapping physical to virtual) and the VM that run on top of the virtuallized hardware [4]
* usually a small os with no drivers , so it is coupled with a linux distro that provides device / hardware access [4]
** the os that the VMM is using for driver's is called the hostOS [6]
*the hostOS provides login and physical access to the hardware as well as management for the VMM [6]
=== VM ===
* the OS that the vm is running is called the guestOS [6]
* the guestOS only sees resources that have been allocated to the VM [6]
==== three approaches ====
*Type I virtualization [5]
** runs off the physical hardware [4]
** Isolation of the guestOs from the hardware is done threw processe level protection meachnism[6]
*** ring 0 = VMM [6]
*** ring 1 = VM [6]
*** this means all instructions from the VM must go threw the VMM [6]
** since there can be multiple VM's on a computer the scheduling is done by the VMM [6]
** on boot the VMM creates a hardware platform for the VM [6]
** load's the VM kernel into virtual memory and then boot's it like a regular computer [6]
** ex. Xen [4]
*Type II virtualization [5]
** run off the host Os [4]
** ex. VMware , QEMU [4]
* Para-virtualization [6]
** Similar to Type but use the HostOs for Device driver access [6]
** Provide a virtualization that is similar to hardware [From the paper posted, no citation yet]
** GuestOS and Hypervisor work together to improve performance

----

Classical Virtualization
* VMMs allow programs in virtual environments to run natively other than resource usage
** Dominant instructions executed directly on cpu
** vmm completely controls system resources
** often need to emulate every native instruction which would severely effect the performance
** sensitive instruction that violate safety and encapsulation
** vmm handles them as priviledged instructions

x86 Virtualization
* virtualization in personal work stations rather than mainframes
** rings that allow isolation between virtual machines
** most privileged in ring 0 and least in ring 3. The operating system runs in ring 0 and user apps in ring 3
*** vmm in ring 0 and vms in lesser privilege rings (1 or 3)
*** guestOS believes its in ring 0
* address space compression, where to run the VMM
** if run using guest address space, guest can find out its virtualized or compromise the isolation
* does not trap all sensitive instructions but can handle them, violates classical virtualization description
* some privileged access fail without faulting
* interrupt virtualization - VMM handles AND guestOS handles
* binary translation - improve performance
* rewriting instructions and trapping before problems arrise

Paravirtualization
* guestOS become exposed to vm information so that the guest is aware that it is virtualized and can make decisions based on this
* allows to avoid problem instructions
* Xen
* guestOS must be modified and is not natively running
**works with the hostOS to run efficiently

VMM types
* hostedVMM - executes in hostOS and uses the drivers and support of the OS
* Stand-aloneVMM - runs directly on hardware and uses it's own drivers and services
* hybridVMM - runs a serviceOS where requests to hardware go through (I/O)

Device Emulation
* implement real hardware in software
* completely virtual device that the guest interacts with
* mapped to physical hardware that handles the interactions but the emulation allows conversion
* allows the vm to be easily migrated between machines as it does not rely on the physical hardware
* allows having multiple vms and simplifies sharing (multiplexing)
* poor performance as the vmm needs to do a lot to virtulize the machine

Paravirtualization
* modified guestOS to cooperate with VMM
* VMM does not have to do everything to handle device drivers
* not everything can be paravirtualized
* proprietary os and device drivers can't be paravirtualized
* still allows an increase in performance
* eventing or callback mechanism
** guestOS modifies interrupt mechs
* modifications are not applicable to all guestOS

Dedicated Devices
* does not virtualize device but assigns directly to guest vm
* uses guest's drivers instead of host
* simplifiest vmm by removing handing of i/o securily
* limited physical devices that can be dedicated
* dificult to migrate vm as it depends on the pairing with this resource
* elims over-head of virtualization and simplicity in vmm
* direct memory access not supported

== Exokernel ==
* Micro-kernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
* Less functionality provided by kernel, security and handling of resource sharing
* Once application receives resource, it can use it as it wishes/in control
* Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware

----
* multiplex resources securely providing protection to mutual distrustful application threw the use of secure binding's[1]
* Goal of the exokernel is to give LibOS maximum freedom with out allowing them to interfere with each other. to do this the exokernel separates protection from management in doing this it provide 3 important tasks[1]
** tracking ownership of resources [1]
** ensuring protection by guarding all resource usage and binding points (not to shure what binding points are)[1]
** revoking access to the resources [1]
* LibrayOS (LibOs)
** Reduces the number of kernel crossings[1]
** Not trusted by the exokernel so can be trusted by the application , Example given is a bad parameter passed to the LibOs only the application is affected.[1] (So LibOs cant interact with kernel ???)
** Any application running on the Exokernel can change the LibrayOs freely [1]
** Application that use LibOS that implement standard interfaces (POSIX) will be portable on any system with the same interface [1]
** LibOs can be made portable if it is designed to interact with a low-level machine independent level to hide hardware details [1]

=== Exokernel Design ===
==== Design Principles ====
*Securely Expose Hardware [1]
** an Exokernel tries to create low level primitives that the hardware resources can be accessed from, this also includes interrupts,exceptions [1]
** the exokernel also export privileged instructions to the LibOS so that traditional OS abstractions can be implemented (eg Process , address pace)[1]
** Exokernels should avoid resource management except when required protection ( allocation , revocation , ownership)[1]
** application based resource management is the best way to build flexible efficient flexible systems [1]
*Expose allocation[1]
** allow LibOs to request physical resources [1]
** resource allocation should not be automatic, the LibOS should participate in every single allocation decision [1]
*Expose Names[1]
** Use physical name's when ever possible[3] (not to sure what physical names are, I think it is as simple as what the hardware is called)--[[User:Asoknack|Asoknack]] 20:27, 9 October 2010 (UTC)
** Physical names capture useful information [3]
*** safer than and less resource intensive than virtual names as no translations are needed[3]
*Expose Revocation [1]
** use visible revocation protocol [1]
** allows well behaved LibOS to preform application level resource management [1]
** Visible revocation allows the LibOS to choose what instance of the resource to release[1](Visible means that when revocation happens the exokernel tell the LibOS that resource is being revoked)
''' Policy '''
* LibOS handle resource policy decisions
* Exokernels have a policy to decided between competing LibOS (Priority , share of resources)
** it enforces this threw allocation and deallocation (every thing can achieved threw this even what block to write and such)

==== Secure Bindings ====
* Used by the exokernel to allow the LibOS to bind to resources [1]
* Allows the separation of protection and resource use [1]
* only checks authorization during bind time [1]
** Application's with complex needs for resources only authorized during bind.[1]
* access checking is done during access time and there is no need to understand complex resources needs during access[1]
** (this means that the exokernel checks once to make sure an application has authorization once approved, when the application tries to use the resource the exokernel is only concerned about policy conflict's)--[[User:Asoknack|Asoknack]] 18:20, 9 October 2010 (UTC)
** allows the kernel to protect the resources with out understanding what the resource is [1]
*three way's to implement
* Hardware Mechanisms [1]
* Software caching [1]
* Downloading application code [1]
''' Downloading Code to the Kernel '''
* used to implement secure bindings , and improve performance[1]
** eliminate the number of kernel crossings [1]
** downloaded code can be run with out the application to be scheduled [2]
==== Visible Resource Revocation ====
* Used for most resources [1]
** allows for LibOS to help with deallocation [1]
** LibOS are able to garner what resources are scare [1]
* Slower than Invisible as application involvement is required [1]
** ex of when invisible is used is Processor addressing-context identifiers [1]
==== Abort Protocol ====
* allows the exokernel to take resources away from the LibOS [1]
* used when the LibOS fails to respond to the revocation request [1]
* Exokernel must be careful not to delete as the LibOS might need to write some system critical data to the resource [1]

== Comparisons ==
====Exokernel/Microkernel====
'''Similarities'''
* Limited functionality in kernel
** functionality in kernel to handle sharing of resources and security
** avoids programming directly to hardware which creates a dependency
* Additional functionality provided in user space as processes
'''Differences'''
* Minimal abstractions provided by the kernel
** Applications given more power in exokernel

====Exokernel/VM====
'''Similarities'''
* Idea of partitioning resources between applications/OSs
* "Control" of resource given
* Isolation from other applications/OSs
'''Differences'''
* Exokernel runs applications, VM runs OS
* VM uses a hostOS and guestOSs run on top
* Virtualization on VMs, Exokernel deals with real resources
* VM hides a lot of information because it emulates. Exokernel does not.

====Microkernel/VM====
'''Differences'''
* With a virtual machine, you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System.
* This can be costly but the benefits are that it's easier and all the standard OS features are available.

== References ==
[1]<nowiki> Engler, D. R., Kaashoek, M. F., and O'Toole, J. 1995. Exokernel: an operating system architecture for application-level resource management. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 251-266. DOI= http://doi.acm.org/10.1145/224056.224076 </nowiki>

[2]<nowiki>Engler, Dawson R. "The Exokernel Operating System Architecture." Diss. Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998. Web. 9 Oct. 2010. <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.61.5054&rep=rep1&type=pdf>.</nowiki>

[3]<nowiki>Kaashoek, M. F., Engler, D. R., Ganger, G. R., Briceño, H. M., Hunt, R., Mazières, D., Pinckney, T., Grimm, R., Jannotti, J., and Mackenzie, K. 1997. Application performance and flexibility on exokernel systems. In Proceedings of the Sixteenth ACM Symposium on Operating Systems Principles (Saint Malo, France, October 05 - 08, 1997). W. M. Waite, Ed. SOSP '97. ACM, New York, NY, 52-65. DOI= http://doi.acm.org/10.1145/268998.266644 </nowiki>

[4]<nowiki>Vallee, G.; Naughton, T.; Engelmann, C.; Hong Ong; Scott, S.L.; , "System-Level Virtualization for High Performance Computing," Parallel, Distributed and Network-Based Processing, 2008. PDP 2008. 16th Euromicro Conference on , vol., no., pp.636-643, 13-15 Feb. 2008
DOI= http://doi.acm.org/10.1109/PDP.2008.85 </nowiki>

[5]<nowiki>Goldberg, R. P. 1973. Architecture of virtual machines. In Proceedings of the Workshop on Virtual Computer Systems (Cambridge, Massachusetts, United States, March 26 - 27, 1973). ACM, New York, NY, 74-112. DOI= http://doi.acm.org/10.1145/800122.803950 </nowiki>

[6]<nowiki>Vallee, G., Naughton, T., and Scott, S. L. 2007. System management software for virtual environments. In Proceedings of the 4th international Conference on Computing Frontiers (Ischia, Italy, May 07 - 09, 2007). CF '07. ACM, New York, NY, 153-160. DOI= http://doi.acm.org/10.1145/1242531.1242555 </nowiki>

[7]<nowiki>Liedtke, J. 1995. On micro-kernel construction. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 237-250. DOI= http://doi.acm.org/10.1145/224056.224075 </nowiki>

[8]<nowiki>Microkernel verses monolithic kernel
http://www.vmars.tuwien.ac.at/courses/akti12/journal/04ss/article_04ss_Roch.pdf - Roch</nowiki>

I will site it/reference it better later

[9]Fisher-Ogden J. 2006. Hardware Support for Efficient Virtualization. University of California, San Diego. http://cseweb.ucsd.edu/~jfisherogden/hardwareVirt.pdf

Not completely sure of the citation style used above.

== Unsorted ==
An overview of exokernels,virtual machines, microkernels *[http://www2.supchurch.org:10999/files/school/classes/CSCI4730/Lectures/grad-structures.ppt Overview](Power Point) 
Should not be used as a source but an overview.

The original paper on [http://portal.acm.org/citation.cfm?id=224076 Exokernels] --[[User:Gautam|Gautam]] 22:39, 6 October 2010 (UTC)

Exokernel-
Minimalistic abstractions for developers
Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs.
Exokernel – fewest hardware abstractions to developer
Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system
Virtual machine is a simulation of any or devices requested by an application program
Exokenel – I’ve got a sound card
Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match
Microkernel – I’ve got sound card that plays Khazikstan sound format only
MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below
-Rovic

Outlining some main features here as I see them.

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have.

I'll locate some references later on. --[[User:Slay|Slay]] 15:00, 7 October 2010 (UTC)

I'm just going to post my answer for question 1 on the individuel assignment and hope it helps. --[[User:Aellebla|Aellebla]] 15:06, 12 October 2010 (UTC)

The design of the micro kernel was to take everything they could out of the Kernel and put it into a process. For ex, networking would be put into a process instead of staying in the kernel. The micro kernel dev's tried to keep lots of things in user space for efficiency. But one major problem with this is there would be a large amount of moving from a process to the kernel to user space and back again and this is a costly, non efficient process.It was an application specific OS, there was no multiplexing. With a virtual machine you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System. This is very heavy however but the benefits are that it‟s easy and all the standard OS features are there whereas in a microkernel setup they would not all be there and this can be seen as a compromise.

Exokernels can be seen as a compromise to virtual machines and microkernels because virtual machines emulate and exokernels do not. When you emulate something you hide a lot of the actual information because you wouldn‟t be able to see the „real‟ hardware. If we look at a virtual box setup running Linux, and we go look at all the hardware, it will be displayed as fake hardware.

Maybe we can have an introduction - paragraph or so on each type - then similarities - differences - and the compromise. I am going to do some research and writing this weekend and I will put some up -- Jslonosky

btw in my page (i guess you can call it that) i have some resources i have found --[[User:Asoknack|Asoknack]] 15:50, 8 October 2010 (UTC)
- Wow, nice man. I will go ahead and write up the descriptive paragraphs on each kernel and virtual machine if no one minds. --Jslonosky

I think we should divide up the paragraphs and proofread each others instead. (Are there only 4 of us?) I don't have much time to work on this today though but I'll try to work on it tomorrow morning. - Slay

Sure guy. That sounds good. There should be 5 or 6 of us though.. . Oh well. Their loss. I will do some before or after work today. Ill start with Microkernel since there is not a large amount of info here, and so we don't overlap each other - JSlonosky

yeah i think there was more like 7 of us btw if any one has any more information feel free to add it would be nice if you add the references so that way citing is really easy on acm.org it will auto give you the citation info (where it says Display Formats click on ACM Ref and new window with the citation info auto pop's up) --[[User:Asoknack|Asoknack]] 02:28, 11 October 2010 (UTC)

I added an outline of the similarities and differences. Add any more that I missed. These are from observations so I don't have any resources. -Slay
That's probably fine. Our textbook probably outlines some of them, so I am sure we can find a few there - JSlonosky

Talked to the teacher today and for VM he said we should focus on the implementation such as Xen and VMware , he also said to talk about para virtualization --[[User:Asoknack|Asoknack]] 18:42, 12 October 2010 (UTC)

A paper about emulation and paravirtualization [http://portal.acm.org/citation.cfm?id=1189289&coll=GUIDE&dl=GUIDE&CFID=105648137&CFTOKEN=47153176&ret=1#Fulltext link] - Slay

Oh no big words. Sorry about the Microkernels not done yet. Working on an outline now. Finally found how to access the ACM through carleton. Gawd.
I am planning an outline, quick bit about kernels in general, (maybe mention monolith kernels?), and what microkernels do.
I see the microkernel outline info and a reference ( Whomever did that == hero: true) about the scheduling and the Memory management. Should that be included in kernels in general and then mention what microkernels build upon/change? - JSlonosky

Sorry late to the party here. My mistake was not checking the discussion page when I checked in. I don't want to trample anyone's current work but I don't see any work on the final essay done. I would love to help just need to know where I can step in so as to not screw anyone else up. -- [[User:Cling|Cling]]

I don't think I'll be able to write up something for the final essay, even though I suggested splitting it. I'll do research tonight though on the paravirtualization. If I find the time, I'll try to write something. Sorry about that. --[[User:Slay|Slay]] 21:52, 13 October 2010 (UTC)

We all have 3004 to do too, man. I do not think anyone has chosen to do Virtual Machine section yet, or the Exokernel itself. But the contrast paragraph and the intro is chosen, and intro is done. Microkernel and kernel will be done in a hour I hope. -- JSlonosky

I can attempt to write up anything, the issue is I don't have any context on what to write, how do I tie it in to the rest of the essay? I only have a Japanese Quiz tomorrow morning then I should be good to write anything up for the rest of the day. As someone who has already written part of the essay, and assuming I attempt the exokernel section, how much do you think I should write? Should it just be about exokernel or should there be comparisons to the other topics? Thanks --[[User:Cling|Cling]] 23:14, 13 October 2010 (UTC)

Go with the Exokernel itself. Slade is getting off work in a hour and we can double check what he is doing then. We can put it together tomorrow sometime, and fill in the other stuff. - JSLonosky

I'll attempt to work on VM tonight, then. I would feel so bad if I didn't write anything. -Slay

Still wondering how much to write, I think we should decide on a decent word count or length so we don't have one short section (which would probably be mine) and/or one massive section that dwarfs all the others. If anyone has already written a section could you post your word count so we can aim to be around there, it would obviously be just a recommendation but it's just better to be on the safe side and have everything uniform. I haven't seen any formal requirements for the essay but I could be wrong, I also haven't been to class in a while. --[[User:Cling|Cling]] 23:33, 13 October 2010 (UTC)

Yeah Slay, VM probably doesnt have much to write about. Get something down, and we can go over it. CLing, Just write what you think. There is not a lot to go over if I write kernel/microkernel well enough. What is a exokernel? exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction, basically (As said by Slade). I will probably end up with 500 or a bit more words. -- JSlonosky

Sound off!

Who's actually reading this? Add your name to the list...

Rovic P.
Jon Slonosky
Corey Ling
Steph Lay
Aaron .L

== The Essay ==

Let's actually breakdown the essay into components then write it here.

I'd like to go along the premise that microkernels and and virtual machines are "weaker" than exokernels in design for the essay. If anyone has any objections, add it here.

-Slade

what do you mean by "weaker"(i think you mean exokernels' takes the best of both worlds ) --[[User:Asoknack|Asoknack]] 02:45, 13 October 2010 (UTC)

What I mean by weaker is that we should focus on the things microkernels and virtual machines may not do as well compared to a system based off an exokernel design and then focus on how an exokenenel can take the best of both worlds. Please choose which section you will work on, that's not to say it'll be the only part you do, but rather we'll all contribute to each part please. 1 day left.
-Slade

...to the extent that exokernels be seen as a compromise between virtual machines and microkernels.
-I'll work on the initial intro. -Slade

3 paragraphs that prove it
Explain how the key design characteristics of these three system architectures compare with each other.

intro/thesis statement -Rovic P.

In Computer Science, the kernel is the component at the center of the majority of operating systems. The kernel is a bridge for applications to access the hardware level. It is responsible for managing the system's resources such as memory, disk storage, task management and networking. We are comparing Exokernels to Microkernels and Virtual Machines by looking at how the kernel goes about such management and its connections. In the Exokernel conceptual model, we can see exokernels become much smaller than microkernels because as this design shows, they are tiny and strive to keep functionality limited to protection and multiplexing of resources. The Virtual Machine Implementation of virtualizing all devices on the system may provide compatibility, but it also adds a layer of complexity within the system. This is less efficient than a real machine as it accesses the hardware indirectly. It can be observed by examining how the exokernel provides low level hardware access and provides custom abstraction to those devices. This is done in order to improve program performance as opposed to a VM's implementation. The exokernel concept has a design that can take the better concepts of microkernels and virtual machines to the extent that exokernels can be seen as a compromise between a virtual machine and a microkernel.

Paragraph 1 -Microkernel -Jon S.

The kernel is the most important part of an operating system. An operating system could not function without the kernel.

A kernel is the lowest level section of an operating system. Within a system, it has the most privileges. It runs along side of the ‘user space’. It is in the ‘user space’ where a user has access. This is also where the user can run its applications and libraries.[8] This leaves the kernel with the need to manage the other necessary processes. For example, the kernel could manage the File Systems and complete process scheduling. The kernel is layered with the most authoritative process on its lowest level.[8] A monolithic kernel, which is a kernel that contains all mandatory processes within itself, was the common kernel type of the earlier versions of today’s operating systems utilized. However, this architecture had problems. [8] If the kernel needed to be updated with more code, or a change in the system, the entire kernel would need to be compiled. Therefore, due to the amount of processes within it, it would take an inefficient amount of time. Here, a microkernel becomes practical.

The concept of a microkernel, is to reduce the code within the kernel. The microkernel is only included in the kernel if it would impact the system. There are a variety of ways the system could be affected if a microkernel were to be implemented, for example, there would be increased performance and efficiency. [7] So, a microkernel is a kernel that has a reduced amount of mandatory software within itself. This means that it contains less software that it has to manage, and has a reduced size. A microkernel that emerged at the end of the 1980’s to the early 1990’s has the structure that processes like the File Systems and the Drivers are removed from it, leaving the kernel with process control and input/out control, and interrupts. [8] This new structure makes the system much more modular, and easier to provide solutions. If a driver must be patched or upgraded, the kernel does not need to be recompiled. [7] The old driver can be removed, and while the device waits for the system to recognize it, the operating system replaces the driver. This lets real-time updating, and it can be done while the computer is still functional. This can reduce the complete crash of the system. If a device fails, the kernel will not crash itself, like a monolithic kernel would. The microkernel can reload the driver of the device that failed and continue functioning. [7]

Want more on the scheduling? I can do that if wanted. -key note on exokernel's mutiplexing vs microkernel's messaging, exo more efficient so perhaps running with the idea that messaging b/w processes not necessarily the ideal way need to also start outlaying weaknesses in the design as well in order to play up the idea that an exokernel just does it better -Slade

Paragraph 2 -Virtual Machine -Steph L.

A Virtual Machine, or VM, is a software abstraction of a physical machine. This entails virtualization of the physical machines resources in order to share them among OS run in the VM. Virtualizing these resources allow the OS to run as if it were on a full machine when, in reality, it is actually running in a virtualized environment on top of a hostOS, the OS actually running on the machine, sharing the resources.

Virtual Machines generally contain two key components, the Virtual Machine Monitor, or VMM and the VM.

The VMM, also known as the hypervisor, manages the virtualization of the physical resources and the interactions with the VM running on top. [4] In other words, it mediates between the virtualized world and the physical world, keeping them separate and monitoring their interactions with each other. The hypervisor is what allows the VM to operate as if it were on its own machine by handling any requests to resources and maintaining these requests with what has actually been provided to the VM by the hostOS. The hostOS provides management for the VMM as well as allowing physical access to devices, hardware and drivers. [6]

The VM is what contains the OS we are running through virtualization. [6] This OS is called the guestOS and it will only be able to access any resources that have been made available to the VM by the hostOS. [6] Otherwise, the guestOS will not know about any other resources and does not have direct access to physical hardware. This will be taken care of by the VMM but the guestOS will execute as its own machine, unaware of this mediator.

There are various ways of implementing hardware virtualization in a system to allow VMs to run. This includes device emulation, paravirtualization and dedicated devices. [9]

In device emulation, the VMM provides a complete virtualization of a device for the guestOS to interact with, in software. [9] The VMM will map this virtualized device to the physical resource and handle any interactions between them. This will usually include converting instructions from the guestOS into instructions that are compatible with the device. [9] Device emulation allows for the VM to be migrated easily to another machine as it is not dependent on the physical devices but on the software emulations instead. [9] It also allows for simpler multiplexing between multiple virtual machines as it can handle sharing though these virtualized devices. [9] A drawback of emulation, however, is poor performance as the VMM must handle every request and convert them to be compatible with the physical device. [9] However, despite its poor performance, emulation is the most common form of virtualization.

Paravirtualization allows for a boost in performance by having the guestOS and the hostOS work together to improve performance. [9] In paravirtualization, the guestOS is not a native OS and must be modified so that it is aware that it is a virtualized system. [9] As the guestOS is aware of this, it can now make better decisions about how it accesses devices. As the guestOS will be able to handle its decisions better, the VMM’s responsibility is reduced as it now does not have to translate between the guestOS and the physical devices. [9] Though the performance boost is a great advantage, there are many disadvantages to this. You can only use paravirtualization if you can implement the modifications to the guestOS. Not everything can be paravirtualized and as such, this limits the cases in which this method can be used. [9] Also, every guestOS must be modified in order to be used in paravirtualization. The modifications will differ in various OS and so, there is also the task of implementing these changes to make a guestOS compatible. [9]

Instead of virtualizing the hardware and mediating between with the VMM, dedicated devices allow mapping directly to the guestOS. [9] In this method, the device will use the guestOS’s drivers instead of the hostOS’s. [9] Using this method allows the guestOS to use the hardware to its full extent without having to deal with the VMM. This simplifies the VMM by eliminating the overhead in virtualizating the hardware and handling the requests to devices. [9] However, there are limited physical resources to be dedicated to a guestOS and this also makes migration difficult as the guestOS is dependent on the physical device. [9]

'''notes'''
- it ended up being quite lengthy. I mainly focused on the device virtualization rather than the architecture of a VM (like x86 virtualization). I'll put up my notes for the paper I found for virtualization. I didn't talk about Xen or VMware though. If any of that is needed, I can try to continue working on it tonight but I have another priority.

-try focusing on the emulation side of VM where emulation's weaknesses vs direct hardware access or custom abstraction that exokernels -Slade

Paragraph 3 -Exokernel -Corey L

Paragraph 4 - Contrast/Compromise --[[User:Asoknack|Asoknack]]

Conclusion - Jon S. - Only a sentence per paragraph, excluding Intro

Sweet. Looks like we got it covered. We should read each others parts and put suggestions and edits. One of us should try and change it to one style if there are contradictions. And to put it on the main page. We can figure that out tomorrow. - Jon S

Once the other parts are up and you see anything you know of as a good reference to back it up, put the link so we can use it. -Slade

I made some edits to the first two paragraphs. I just reworded some of the unclear sentences and some grammatical errors. I'll work on editing more of it after comp 3007. Also when all the parts are up i can go through it and link the paragraphs together so it can be read more like an essay --[[User:Aellebla|Aellebla]] 15:18, 14 October 2010 (UTC)

==Potential Test Questions==

Add potential test questions here:

Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-14T16:00:49Z

Slay:

== Microkernel ==
* Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
* Keep basic functionality in kernel to handle sharing of resources
* Separation allows for manageability and security, corruption in one does not necessarily cause failure in system
* Large amount of moving from a process to Kernel to user space and back again, this is a costly operation.

----

''' Microkernel '''
* try's to minimize the amount of software that is mandatory or required [7]
advantages of Microkernel
* favors a modular system structure [7]
* one failure of a program does not impact any other programs [7]
* can support more than one api or strategies since all programs are separated [7]
==== Microkernel Concepts ====
* piece of code is allowed in the kernel only if moving it outside the kernel would adversely affect the system. [7]
* any subsystem program created must be independent of all other subsystem's, any subsystem that is used can guarantee this from all other subsystems [7]
===== Address Space =====
* a mapping that relates the physical page to the virtual page. [7]
* processor specific [7]
* hide's the hardware's concept of address space [7]
* based off the idea of recursion each subsystem has it's own address space [7]
* the micro kernel provides 3 operations [7]
** Grant [7]
*** allows the owner to give a page to a recipient, provided the recipient want's it the page is removed from the owner's address space and but in the recipients. [7]
*** must be available to the owner. [7]
** Map [7]
*** allows the user to share a page with a recipient [7]
*** page is not removed from the owner's address space. [7]
** Flush [7]
*** remove's the page from all recipients address space [7]
*** how does this work with Grant --[[User:Asoknack|Asoknack]] 19:10, 12 October 2010 (UTC)
* allows memory management and paging out side the kernel
* Map and flush is required for memory manger's and pagers [7]
* can be used to implement access right's [7]
* controlling I/O Right's and driver's are not done at kernel level [7]

===== Thread's IPC =====
* Threads
** in the kernel [7]
** Since a thread has an address space , all changes to the thread need to be done by the kernel [7]
* IPC [7]
** in the kernel IPC
** grant and map also need IPC (So buye the priciple above this has to be in the kernel)[7]
** basic way for sub process to communicate. [7]
* Interrupts
** partially in the kernel [7]
** hard ware is a set of thread's which are empty except for there unique sender id [7]
** transformation of the message to the interrupt is done in the kernel [7]
** the kernel is not involved in device - specific interrupt's and does not understand the interrupt. [7]
*** resting the interrupt is done at user level [7]
** if a privileged command is need it is done implicitly the next time an IPC command is sent from the device [7]

===== Unique Identifiers =====

== Virtual Machine ==
* Partitioning or virtualizing resources among OS virtualization running on top of host OS
* Virtualized OS believe running on full machine on its own

----
System Level Virtualization

=== VMM ===
* stands for Virtual Machine Monitor, also known as the hyper-visor[4]
* responsible for virtualization of hardware(mapping physical to virtual) and the VM that run on top of the virtuallized hardware [4]
* usually a small os with no drivers , so it is coupled with a linux distro that provides device / hardware access [4]
** the os that the VMM is using for driver's is called the hostOS [6]
*the hostOS provides login and physical access to the hardware as well as management for the VMM [6]
=== VM ===
* the OS that the vm is running is called the guestOS [6]
* the guestOS only sees resources that have been allocated to the VM [6]
==== three approaches ====
*Type I virtualization [5]
** runs off the physical hardware [4]
** Isolation of the guestOs from the hardware is done threw processe level protection meachnism[6]
*** ring 0 = VMM [6]
*** ring 1 = VM [6]
*** this means all instructions from the VM must go threw the VMM [6]
** since there can be multiple VM's on a computer the scheduling is done by the VMM [6]
** on boot the VMM creates a hardware platform for the VM [6]
** load's the VM kernel into virtual memory and then boot's it like a regular computer [6]
** ex. Xen [4]
*Type II virtualization [5]
** run off the host Os [4]
** ex. VMware , QEMU [4]
* Para-virtualization [6]
** Similar to Type but use the HostOs for Device driver access [6]
** Provide a virtualization that is similar to hardware [From the paper posted, no citation yet]
** GuestOS and Hypervisor work together to improve performance
---
Classical Virtualization
* VMMs allow programs in virtual environments to run natively other than resource usage
** Dominant instructions executed directly on cpu
** vmm completely controls system resources
** often need to emulate every native instruction which would severely effect the performance
** sensitive instruction that violate safety and encapsulation
** vmm handles them as priviledged instructions

x86 Virtualization
* virtualization in personal work stations rather than mainframes
** rings that allow isolation between virtual machines
** most privileged in ring 0 and least in ring 3. The operating system runs in ring 0 and user apps in ring 3
*** vmm in ring 0 and vms in lesser privilege rings (1 or 3)
*** guestOS believes its in ring 0
* address space compression, where to run the VMM
** if run using guest address space, guest can find out its virtualized or compromise the isolation
* does not trap all sensitive instructions but can handle them, violates classical virtualization description
* some privileged access fail without faulting
* interrupt virtualization - VMM handles AND guestOS handles
* binary translation - improve performance
* rewriting instructions and trapping before problems arrise

Paravirtualization
* guestOS become exposed to vm information so that the guest is aware that it is virtualized and can make decisions based on this
* allows to avoid problem instructions
* Xen
* guestOS must be modified and is not natively running
**works with the hostOS to run efficiently

VMM types
* hostedVMM - executes in hostOS and uses the drivers and support of the OS
* Stand-aloneVMM - runs directly on hardware and uses it's own drivers and services
* hybridVMM - runs a serviceOS where requests to hardware go through (I/O)

Device Emulation
* implement real hardware in software
* completely virtual device that the guest interacts with
* mapped to physical hardware that handles the interactions but the emulation allows conversion
* allows the vm to be easily migrated between machines as it does not rely on the physical hardware
* allows having multiple vms and simplifies sharing (multiplexing)
* poor performance as the vmm needs to do a lot to virtulize the machine

Paravirtualization
* modified guestOS to cooperate with VMM
* VMM does not have to do everything to handle device drivers
* not everything can be paravirtualized
* proprietary os and device drivers can't be paravirtualized
* still allows an increase in performance
* eventing or callback mechanism
** guestOS modifies interrupt mechs
* modifications are not applicable to all guestOS

Dedicated Devices
* does not virtualize device but assigns directly to guest vm
* uses guest's drivers instead of host
* simplifiest vmm by removing handing of i/o securily
* limited physical devices that can be dedicated
* dificult to migrate vm as it depends on the pairing with this resource
* elims over-head of virtualization and simplicity in vmm
* direct memory access not supported

== Exokernel ==
* Micro-kernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
* Less functionality provided by kernel, security and handling of resource sharing
* Once application receives resource, it can use it as it wishes/in control
* Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware

----
* multiplex resources securely providing protection to mutual distrustful application threw the use of secure binding's[1]
* Goal of the exokernel is to give LibOS maximum freedom with out allowing them to interfere with each other. to do this the exokernel separates protection from management in doing this it provide 3 important tasks[1]
** tracking ownership of resources [1]
** ensuring protection by guarding all resource usage and binding points (not to shure what binding points are)[1]
** revoking access to the resources [1]
* LibrayOS (LibOs)
** Reduces the number of kernel crossings[1]
** Not trusted by the exokernel so can be trusted by the application , Example given is a bad parameter passed to the LibOs only the application is affected.[1] (So LibOs cant interact with kernel ???)
** Any application running on the Exokernel can change the LibrayOs freely [1]
** Application that use LibOS that implement standard interfaces (POSIX) will be portable on any system with the same interface [1]
** LibOs can be made portable if it is designed to interact with a low-level machine independent level to hide hardware details [1]

=== Exokernel Design ===
==== Design Principles ====
*Securely Expose Hardware [1]
** an Exokernel tries to create low level primitives that the hardware resources can be accessed from, this also includes interrupts,exceptions [1]
** the exokernel also export privileged instructions to the LibOS so that traditional OS abstractions can be implemented (eg Process , address pace)[1]
** Exokernels should avoid resource management except when required protection ( allocation , revocation , ownership)[1]
** application based resource management is the best way to build flexible efficient flexible systems [1]
*Expose allocation[1]
** allow LibOs to request physical resources [1]
** resource allocation should not be automatic, the LibOS should participate in every single allocation decision [1]
*Expose Names[1]
** Use physical name's when ever possible[3] (not to sure what physical names are, I think it is as simple as what the hardware is called)--[[User:Asoknack|Asoknack]] 20:27, 9 October 2010 (UTC)
** Physical names capture useful information [3]
*** safer than and less resource intensive than virtual names as no translations are needed[3]
*Expose Revocation [1]
** use visible revocation protocol [1]
** allows well behaved LibOS to preform application level resource management [1]
** Visible revocation allows the LibOS to choose what instance of the resource to release[1](Visible means that when revocation happens the exokernel tell the LibOS that resource is being revoked)
''' Policy '''
* LibOS handle resource policy decisions
* Exokernels have a policy to decided between competing LibOS (Priority , share of resources)
** it enforces this threw allocation and deallocation (every thing can achieved threw this even what block to write and such)

==== Secure Bindings ====
* Used by the exokernel to allow the LibOS to bind to resources [1]
* Allows the separation of protection and resource use [1]
* only checks authorization during bind time [1]
** Application's with complex needs for resources only authorized during bind.[1]
* access checking is done during access time and there is no need to understand complex resources needs during access[1]
** (this means that the exokernel checks once to make sure an application has authorization once approved, when the application tries to use the resource the exokernel is only concerned about policy conflict's)--[[User:Asoknack|Asoknack]] 18:20, 9 October 2010 (UTC)
** allows the kernel to protect the resources with out understanding what the resource is [1]
*three way's to implement
* Hardware Mechanisms [1]
* Software caching [1]
* Downloading application code [1]
''' Downloading Code to the Kernel '''
* used to implement secure bindings , and improve performance[1]
** eliminate the number of kernel crossings [1]
** downloaded code can be run with out the application to be scheduled [2]
==== Visible Resource Revocation ====
* Used for most resources [1]
** allows for LibOS to help with deallocation [1]
** LibOS are able to garner what resources are scare [1]
* Slower than Invisible as application involvement is required [1]
** ex of when invisible is used is Processor addressing-context identifiers [1]
==== Abort Protocol ====
* allows the exokernel to take resources away from the LibOS [1]
* used when the LibOS fails to respond to the revocation request [1]
* Exokernel must be careful not to delete as the LibOS might need to write some system critical data to the resource [1]

== Comparisons ==
====Exokernel/Microkernel====
'''Similarities'''
* Limited functionality in kernel
** functionality in kernel to handle sharing of resources and security
** avoids programming directly to hardware which creates a dependency
* Additional functionality provided in user space as processes
'''Differences'''
* Minimal abstractions provided by the kernel
** Applications given more power in exokernel

====Exokernel/VM====
'''Similarities'''
* Idea of partitioning resources between applications/OSs
* "Control" of resource given
* Isolation from other applications/OSs
'''Differences'''
* Exokernel runs applications, VM runs OS
* VM uses a hostOS and guestOSs run on top
* Virtualization on VMs, Exokernel deals with real resources
* VM hides a lot of information because it emulates. Exokernel does not.

====Microkernel/VM====
'''Differences'''
* With a virtual machine, you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System.
* This can be costly but the benefits are that it's easier and all the standard OS features are available.

== References ==
[1]<nowiki> Engler, D. R., Kaashoek, M. F., and O'Toole, J. 1995. Exokernel: an operating system architecture for application-level resource management. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 251-266. DOI= http://doi.acm.org/10.1145/224056.224076 </nowiki>

[2]<nowiki>Engler, Dawson R. "The Exokernel Operating System Architecture." Diss. Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998. Web. 9 Oct. 2010. <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.61.5054&rep=rep1&type=pdf>.</nowiki>

[3]<nowiki>Kaashoek, M. F., Engler, D. R., Ganger, G. R., Briceño, H. M., Hunt, R., Mazières, D., Pinckney, T., Grimm, R., Jannotti, J., and Mackenzie, K. 1997. Application performance and flexibility on exokernel systems. In Proceedings of the Sixteenth ACM Symposium on Operating Systems Principles (Saint Malo, France, October 05 - 08, 1997). W. M. Waite, Ed. SOSP '97. ACM, New York, NY, 52-65. DOI= http://doi.acm.org/10.1145/268998.266644 </nowiki>

[4]<nowiki>Vallee, G.; Naughton, T.; Engelmann, C.; Hong Ong; Scott, S.L.; , "System-Level Virtualization for High Performance Computing," Parallel, Distributed and Network-Based Processing, 2008. PDP 2008. 16th Euromicro Conference on , vol., no., pp.636-643, 13-15 Feb. 2008
DOI= http://doi.acm.org/10.1109/PDP.2008.85 </nowiki>

[5]<nowiki>Goldberg, R. P. 1973. Architecture of virtual machines. In Proceedings of the Workshop on Virtual Computer Systems (Cambridge, Massachusetts, United States, March 26 - 27, 1973). ACM, New York, NY, 74-112. DOI= http://doi.acm.org/10.1145/800122.803950 </nowiki>

[6]<nowiki>Vallee, G., Naughton, T., and Scott, S. L. 2007. System management software for virtual environments. In Proceedings of the 4th international Conference on Computing Frontiers (Ischia, Italy, May 07 - 09, 2007). CF '07. ACM, New York, NY, 153-160. DOI= http://doi.acm.org/10.1145/1242531.1242555 </nowiki>

[7]<nowiki>Liedtke, J. 1995. On micro-kernel construction. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 237-250. DOI= http://doi.acm.org/10.1145/224056.224075 </nowiki>

[8]<nowiki>Microkernel verses monolithic kernel
http://www.vmars.tuwien.ac.at/courses/akti12/journal/04ss/article_04ss_Roch.pdf - Roch</nowiki>

I will site it/reference it better later

[9]Fisher-Ogden J. 2006. Hardware Support for Efficient Virtualization. University of California, San Diego. http://cseweb.ucsd.edu/~jfisherogden/hardwareVirt.pdf

Not completely sure of the citation style used above.

== Unsorted ==
An overview of exokernels,virtual machines, microkernels *[http://www2.supchurch.org:10999/files/school/classes/CSCI4730/Lectures/grad-structures.ppt Overview](Power Point) 
Should not be used as a source but an overview.

The original paper on [http://portal.acm.org/citation.cfm?id=224076 Exokernels] --[[User:Gautam|Gautam]] 22:39, 6 October 2010 (UTC)

Exokernel-
Minimalistic abstractions for developers
Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs.
Exokernel – fewest hardware abstractions to developer
Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system
Virtual machine is a simulation of any or devices requested by an application program
Exokenel – I’ve got a sound card
Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match
Microkernel – I’ve got sound card that plays Khazikstan sound format only
MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below
-Rovic

Outlining some main features here as I see them.

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have.

I'll locate some references later on. --[[User:Slay|Slay]] 15:00, 7 October 2010 (UTC)

I'm just going to post my answer for question 1 on the individuel assignment and hope it helps. --[[User:Aellebla|Aellebla]] 15:06, 12 October 2010 (UTC)

The design of the micro kernel was to take everything they could out of the Kernel and put it into a process. For ex, networking would be put into a process instead of staying in the kernel. The micro kernel dev's tried to keep lots of things in user space for efficiency. But one major problem with this is there would be a large amount of moving from a process to the kernel to user space and back again and this is a costly, non efficient process.It was an application specific OS, there was no multiplexing. With a virtual machine you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System. This is very heavy however but the benefits are that it‟s easy and all the standard OS features are there whereas in a microkernel setup they would not all be there and this can be seen as a compromise.

Exokernels can be seen as a compromise to virtual machines and microkernels because virtual machines emulate and exokernels do not. When you emulate something you hide a lot of the actual information because you wouldn‟t be able to see the „real‟ hardware. If we look at a virtual box setup running Linux, and we go look at all the hardware, it will be displayed as fake hardware.

Maybe we can have an introduction - paragraph or so on each type - then similarities - differences - and the compromise. I am going to do some research and writing this weekend and I will put some up -- Jslonosky

btw in my page (i guess you can call it that) i have some resources i have found --[[User:Asoknack|Asoknack]] 15:50, 8 October 2010 (UTC)
- Wow, nice man. I will go ahead and write up the descriptive paragraphs on each kernel and virtual machine if no one minds. --Jslonosky

I think we should divide up the paragraphs and proofread each others instead. (Are there only 4 of us?) I don't have much time to work on this today though but I'll try to work on it tomorrow morning. - Slay

Sure guy. That sounds good. There should be 5 or 6 of us though.. . Oh well. Their loss. I will do some before or after work today. Ill start with Microkernel since there is not a large amount of info here, and so we don't overlap each other - JSlonosky

yeah i think there was more like 7 of us btw if any one has any more information feel free to add it would be nice if you add the references so that way citing is really easy on acm.org it will auto give you the citation info (where it says Display Formats click on ACM Ref and new window with the citation info auto pop's up) --[[User:Asoknack|Asoknack]] 02:28, 11 October 2010 (UTC)

I added an outline of the similarities and differences. Add any more that I missed. These are from observations so I don't have any resources. -Slay
That's probably fine. Our textbook probably outlines some of them, so I am sure we can find a few there - JSlonosky

Talked to the teacher today and for VM he said we should focus on the implementation such as Xen and VMware , he also said to talk about para virtualization --[[User:Asoknack|Asoknack]] 18:42, 12 October 2010 (UTC)

A paper about emulation and paravirtualization [http://portal.acm.org/citation.cfm?id=1189289&coll=GUIDE&dl=GUIDE&CFID=105648137&CFTOKEN=47153176&ret=1#Fulltext link] - Slay

Oh no big words. Sorry about the Microkernels not done yet. Working on an outline now. Finally found how to access the ACM through carleton. Gawd.
I am planning an outline, quick bit about kernels in general, (maybe mention monolith kernels?), and what microkernels do.
I see the microkernel outline info and a reference ( Whomever did that == hero: true) about the scheduling and the Memory management. Should that be included in kernels in general and then mention what microkernels build upon/change? - JSlonosky

Sorry late to the party here. My mistake was not checking the discussion page when I checked in. I don't want to trample anyone's current work but I don't see any work on the final essay done. I would love to help just need to know where I can step in so as to not screw anyone else up. -- [[User:Cling|Cling]]

I don't think I'll be able to write up something for the final essay, even though I suggested splitting it. I'll do research tonight though on the paravirtualization. If I find the time, I'll try to write something. Sorry about that. --[[User:Slay|Slay]] 21:52, 13 October 2010 (UTC)

We all have 3004 to do too, man. I do not think anyone has chosen to do Virtual Machine section yet, or the Exokernel itself. But the contrast paragraph and the intro is chosen, and intro is done. Microkernel and kernel will be done in a hour I hope. -- JSlonosky

I can attempt to write up anything, the issue is I don't have any context on what to write, how do I tie it in to the rest of the essay? I only have a Japanese Quiz tomorrow morning then I should be good to write anything up for the rest of the day. As someone who has already written part of the essay, and assuming I attempt the exokernel section, how much do you think I should write? Should it just be about exokernel or should there be comparisons to the other topics? Thanks --[[User:Cling|Cling]] 23:14, 13 October 2010 (UTC)

Go with the Exokernel itself. Slade is getting off work in a hour and we can double check what he is doing then. We can put it together tomorrow sometime, and fill in the other stuff. - JSLonosky

I'll attempt to work on VM tonight, then. I would feel so bad if I didn't write anything. -Slay

Still wondering how much to write, I think we should decide on a decent word count or length so we don't have one short section (which would probably be mine) and/or one massive section that dwarfs all the others. If anyone has already written a section could you post your word count so we can aim to be around there, it would obviously be just a recommendation but it's just better to be on the safe side and have everything uniform. I haven't seen any formal requirements for the essay but I could be wrong, I also haven't been to class in a while. --[[User:Cling|Cling]] 23:33, 13 October 2010 (UTC)

Yeah Slay, VM probably doesnt have much to write about. Get something down, and we can go over it. CLing, Just write what you think. There is not a lot to go over if I write kernel/microkernel well enough. What is a exokernel? exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction, basically (As said by Slade). I will probably end up with 500 or a bit more words. -- JSlonosky

Sound off!

Who's actually reading this? Add your name to the list...

Rovic P.
Jon Slonosky
Corey Ling
Steph Lay
Aaron .L

== The Essay ==

Let's actually breakdown the essay into components then write it here.

I'd like to go along the premise that microkernels and and virtual machines are "weaker" than exokernels in design for the essay. If anyone has any objections, add it here.

-Slade

what do you mean by "weaker"(i think you mean exokernels' takes the best of both worlds ) --[[User:Asoknack|Asoknack]] 02:45, 13 October 2010 (UTC)

What I mean by weaker is that we should focus on the things microkernels and virtual machines may not do as well compared to a system based off an exokernel design and then focus on how an exokenenel can take the best of both worlds. Please choose which section you will work on, that's not to say it'll be the only part you do, but rather we'll all contribute to each part please. 1 day left.
-Slade

...to the extent that exokernels be seen as a compromise between virtual machines and microkernels.
-I'll work on the initial intro. -Slade

3 paragraphs that prove it
Explain how the key design characteristics of these three system architectures compare with each other.

intro/thesis statement -Rovic P.

In Computer Science, the kernel is the component at the center of the majority of operating systems. The kernel is a bridge for applications to access the hardware level. It is responsible for managing the system's resources such as memory, disk storage, task management and networking. We are comparing Exokernels to Microkernels and Virtual Machines by looking at how the kernel goes about such management and its connections. In the Exokernel conceptual model, we can see exokernels become much smaller than microkernels because as this design shows, they are tiny and strive to keep functionality limited to protection and multiplexing of resources. The Virtual Machine Implementation of virtualizing all devices on the system may provide compatibility, but it also adds a layer of complexity within the system. This is less efficient than a real machine as it accesses the hardware indirectly. It can be observed by examining how the exokernel provides low level hardware access and provides custom abstraction to those devices. This is done in order to improve program performance as opposed to a VM's implementation. The exokernel concept has a design that can take the better concepts of microkernels and virtual machines to the extent that exokernels can be seen as a compromise between a virtual machine and a microkernel.

Paragraph 1 -Microkernel -Jon S.

The kernel is the most important part of an operating system. An operating system could not function without the kernel.

A kernel is the lowest level section of an operating system. Within a system, it has the most privileges. It runs along side of the ‘user space’. It is in the ‘user space’ where a user has access. This is also where the user can run its applications and libraries.[8] This leaves the kernel with the need to manage the other necessary processes. For example, the kernel could manage the File Systems and complete process scheduling. The kernel is layered with the most authoritative process on its lowest level.[8] A monolithic kernel, which is a kernel that contains all mandatory processes within itself, was the common kernel type of the earlier versions of today’s operating systems utilized. However, this architecture had problems. [8] If the kernel needed to be updated with more code, or a change in the system, the entire kernel would need to be compiled. Therefore, due to the amount of processes within it, it would take an inefficient amount of time. Here, a microkernel becomes practical.

The concept of a microkernel, is to reduce the code within the kernel. The microkernel is only included in the kernel if it would impact the system. There are a variety of ways the system could be affected if a microkernel were to be implemented, for example, there would be increased performance and efficiency. [7] So, a microkernel is a kernel that has a reduced amount of mandatory software within itself. This means that it contains less software that it has to manage, and has a reduced size. A microkernel that emerged at the end of the 1980’s to the early 1990’s has the structure that processes like the File Systems and the Drivers are removed from it, leaving the kernel with process control and input/out control, and interrupts. [8] This new structure makes the system much more modular, and easier to provide solutions. If a driver must be patched or upgraded, the kernel does not need to be recompiled. [7] The old driver can be removed, and while the device waits for the system to recognize it, the operating system replaces the driver. This lets real-time updating, and it can be done while the computer is still functional. This can reduce the complete crash of the system. If a device fails, the kernel will not crash itself, like a monolithic kernel would. The microkernel can reload the driver of the device that failed and continue functioning. [7]

Want more on the scheduling? I can do that if wanted. -key note on exokernel's mutiplexing vs microkernel's messaging, exo more efficient so perhaps running with the idea that messaging b/w processes not necessarily the ideal way need to also start outlaying weaknesses in the design as well in order to play up the idea that an exokernel just does it better -Slade

Paragraph 2 -Virtual Machine -Steph L.

A Virtual Machine, or VM, is a software abstraction of a physical machine. This entails virtualization of the physical machines resources in order to share them among OS run in the VM. Virtualizing these resources allow the OS to run as if it were on a full machine when, in reality, it is actually running in a virtualized environment on top of a hostOS, the OS actually running on the machine, sharing the resources.

Virtual Machines generally contain two key components, the Virtual Machine Monitor, or VMM and the VM.

The VMM, also known as the hypervisor, manages the virtualization of the physical resources and the interactions with the VM running on top. [4] In other words, it mediates between the virtualized world and the physical world, keeping them separate and monitoring their interactions with each other. The hypervisor is what allows the VM to operate as if it were on its own machine by handling any requests to resources and maintaining these requests with what has actually been provided to the VM by the hostOS. The hostOS provides management for the VMM as well as allowing physical access to devices, hardware and drivers. [6]

The VM is what contains the OS we are running through virtualization. [6] This OS is called the guestOS and it will only be able to access any resources that have been made available to the VM by the hostOS. [6] Otherwise, the guestOS will not know about any other resources and does not have direct access to physical hardware. This will be taken care of by the VMM but the guestOS will execute as its own machine, unaware of this mediator.

There are various ways of implementing hardware virtualization in a system to allow VMs to run. This includes device emulation, paravirtualization and dedicated devices. [9]

In device emulation, the VMM provides a complete virtualization of a device for the guestOS to interact with, in software. [9] The VMM will map this virtualized device to the physical resource and handle any interactions between them. This will usually include converting instructions from the guestOS into instructions that are compatible with the device. [9] Device emulation allows for the VM to be migrated easily to another machine as it is not dependent on the physical devices but on the software emulations instead. [9] It also allows for simpler multiplexing between multiple virtual machines as it can handle sharing though these virtualized devices. [9] A drawback of emulation, however, is poor performance as the VMM must handle every request and convert them to be compatible with the physical device. [9] However, despite its poor performance, emulation is the most common form of virtualization.

Paravirtualization allows for a boost in performance by having the guestOS and the hostOS work together to improve performance. [9] In paravirtualization, the guestOS is not a native OS and must be modified so that it is aware that it is a virtualized system. [9] As the guestOS is aware of this, it can now make better decisions about how it accesses devices. As the guestOS will be able to handle its decisions better, the VMM’s responsibility is reduced as it now does not have to translate between the guestOS and the physical devices. [9] Though the performance boost is a great advantage, there are many disadvantages to this. You can only use paravirtualization if you can implement the modifications to the guestOS. Not everything can be paravirtualized and as such, this limits the cases in which this method can be used. [9] Also, every guestOS must be modified in order to be used in paravirtualization. The modifications will differ in various OS and so, there is also the task of implementing these changes to make a guestOS compatible. [9]

Instead of virtualizing the hardware and mediating between with the VMM, dedicated devices allow mapping directly to the guestOS. [9] In this method, the device will use the guestOS’s drivers instead of the hostOS’s. [9] Using this method allows the guestOS to use the hardware to its full extent without having to deal with the VMM. This simplifies the VMM by eliminating the overhead in virtualizating the hardware and handling the requests to devices. [9] However, there are limited physical resources to be dedicated to a guestOS and this also makes migration difficult as the guestOS is dependent on the physical device. [9]

'''notes'''
- it ended up being quite lengthy. I mainly focused on the device virtualization rather than the architecture of a VM (like x86 virtualization). I'll put up my notes for the paper I found for virtualization. I didn't talk about Xen or VMware though. If any of that is needed, I can try to continue working on it tonight but I have another priority.

-try focusing on the emulation side of VM where emulation's weaknesses vs direct hardware access or custom abstraction that exokernels -Slade

Paragraph 3 -Exokernel -Corey L

Paragraph 4 - Contrast/Compromise --[[User:Asoknack|Asoknack]]

Conclusion - Jon S. - Only a sentence per paragraph, excluding Intro

Sweet. Looks like we got it covered. We should read each others parts and put suggestions and edits. One of us should try and change it to one style if there are contradictions. And to put it on the main page. We can figure that out tomorrow. - Jon S

Once the other parts are up and you see anything you know of as a good reference to back it up, put the link so we can use it. -Slade

I made some edits to the first two paragraphs. I just reworded some of the unclear sentences and some grammatical errors. I'll work on editing more of it after comp 3007. Also when all the parts are up i can go through it and link the paragraphs together so it can be read more like an essay --[[User:Aellebla|Aellebla]] 15:18, 14 October 2010 (UTC)

==Potential Test Questions==

Add potential test questions here:

Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-14T04:24:30Z

Slay: /* The Essay */

== Microkernel ==
* Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
* Keep basic functionality in kernel to handle sharing of resources
* Separation allows for manageability and security, corruption in one does not necessarily cause failure in system
* Large amount of moving from a process to Kernel to user space and back again, this is a costly operation.

----

''' Microkernel '''
* try's to minimize the amount of software that is mandatory or required [7]
advantages of Microkernel
* favors a modular system structure [7]
* one failure of a program does not impact any other programs [7]
* can support more than one api or strategies since all programs are separated [7]
==== Microkernel Concepts ====
* piece of code is allowed in the kernel only if moving it outside the kernel would adversely affect the system. [7]
* any subsystem program created must be independent of all other subsystem's, any subsystem that is used can guarantee this from all other subsystems [7]
===== Address Space =====
* a mapping that relates the physical page to the virtual page. [7]
* processor specific [7]
* hide's the hardware's concept of address space [7]
* based off the idea of recursion each subsystem has it's own address space [7]
* the micro kernel provides 3 operations [7]
** Grant [7]
*** allows the owner to give a page to a recipient, provided the recipient want's it the page is removed from the owner's address space and but in the recipients. [7]
*** must be available to the owner. [7]
** Map [7]
*** allows the user to share a page with a recipient [7]
*** page is not removed from the owner's address space. [7]
** Flush [7]
*** remove's the page from all recipients address space [7]
*** how does this work with Grant --[[User:Asoknack|Asoknack]] 19:10, 12 October 2010 (UTC)
* allows memory management and paging out side the kernel
* Map and flush is required for memory manger's and pagers [7]
* can be used to implement access right's [7]
* controlling I/O Right's and driver's are not done at kernel level [7]

===== Thread's IPC =====
* Threads
** in the kernel [7]
** Since a thread has an address space , all changes to the thread need to be done by the kernel [7]
* IPC [7]
** in the kernel IPC
** grant and map also need IPC (So buye the priciple above this has to be in the kernel)[7]
** basic way for sub process to communicate. [7]
* Interrupts
** partially in the kernel [7]
** hard ware is a set of thread's which are empty except for there unique sender id [7]
** transformation of the message to the interrupt is done in the kernel [7]
** the kernel is not involved in device - specific interrupt's and does not understand the interrupt. [7]
*** resting the interrupt is done at user level [7]
** if a privileged command is need it is done implicitly the next time an IPC command is sent from the device [7]

===== Unique Identifiers =====

== Virtual Machine ==
* Partitioning or virtualizing resources among OS virtualization running on top of host OS
* Virtualized OS believe running on full machine on its own

----
System Level Virtualization

=== VMM ===
* stands for Virtual Machine Monitor, also known as the hyper-visor[4]
* responsible for virtualization of hardware(mapping physical to virtual) and the VM that run on top of the virtuallized hardware [4]
* usually a small os with no drivers , so it is coupled with a linux distro that provides device / hardware access [4]
** the os that the VMM is using for driver's is called the hostOS [6]
*the hostOS provides login and physical access to the hardware as well as management for the VMM [6]
=== VM ===
* the OS that the vm is running is called the guestOS [6]
* the guestOS only sees resources that have been allocated to the VM [6]
==== three approaches ====
*Type I virtualization [5]
** runs off the physical hardware [4]
** Isolation of the guestOs from the hardware is done threw processe level protection meachnism[6]
*** ring 0 = VMM [6]
*** ring 1 = VM [6]
*** this means all instructions from the VM must go threw the VMM [6]
** since there can be multiple VM's on a computer the scheduling is done by the VMM [6]
** on boot the VMM creates a hardware platform for the VM [6]
** load's the VM kernel into virtual memory and then boot's it like a regular computer [6]
** ex. Xen [4]
*Type II virtualization [5]
** run off the host Os [4]
** ex. VMware , QEMU [4]
* Para-virtualization [6]
** Similar to Type but use the HostOs for Device driver access [6]
** Provide a virtualization that is similar to hardware [From the paper posted, no citation yet]
** GuestOS and Hypervisor work together to improve performance

== Exokernel ==
* Micro-kernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
* Less functionality provided by kernel, security and handling of resource sharing
* Once application receives resource, it can use it as it wishes/in control
* Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware

----
* multiplex resources securely providing protection to mutual distrustful application threw the use of secure binding's[1]
* Goal of the exokernel is to give LibOS maximum freedom with out allowing them to interfere with each other. to do this the exokernel separates protection from management in doing this it provide 3 important tasks[1]
** tracking ownership of resources [1]
** ensuring protection by guarding all resource usage and binding points (not to shure what binding points are)[1]
** revoking access to the resources [1]
* LibrayOS (LibOs)
** Reduces the number of kernel crossings[1]
** Not trusted by the exokernel so can be trusted by the application , Example given is a bad parameter passed to the LibOs only the application is affected.[1] (So LibOs cant interact with kernel ???)
** Any application running on the Exokernel can change the LibrayOs freely [1]
** Application that use LibOS that implement standard interfaces (POSIX) will be portable on any system with the same interface [1]
** LibOs can be made portable if it is designed to interact with a low-level machine independent level to hide hardware details [1]

=== Exokernel Design ===
==== Design Principles ====
*Securely Expose Hardware [1]
** an Exokernel tries to create low level primitives that the hardware resources can be accessed from, this also includes interrupts,exceptions [1]
** the exokernel also export privileged instructions to the LibOS so that traditional OS abstractions can be implemented (eg Process , address pace)[1]
** Exokernels should avoid resource management except when required protection ( allocation , revocation , ownership)[1]
** application based resource management is the best way to build flexible efficient flexible systems [1]
*Expose allocation[1]
** allow LibOs to request physical resources [1]
** resource allocation should not be automatic, the LibOS should participate in every single allocation decision [1]
*Expose Names[1]
** Use physical name's when ever possible[3] (not to sure what physical names are, I think it is as simple as what the hardware is called)--[[User:Asoknack|Asoknack]] 20:27, 9 October 2010 (UTC)
** Physical names capture useful information [3]
*** safer than and less resource intensive than virtual names as no translations are needed[3]
*Expose Revocation [1]
** use visible revocation protocol [1]
** allows well behaved LibOS to preform application level resource management [1]
** Visible revocation allows the LibOS to choose what instance of the resource to release[1](Visible means that when revocation happens the exokernel tell the LibOS that resource is being revoked)
''' Policy '''
* LibOS handle resource policy decisions
* Exokernels have a policy to decided between competing LibOS (Priority , share of resources)
** it enforces this threw allocation and deallocation (every thing can achieved threw this even what block to write and such)

==== Secure Bindings ====
* Used by the exokernel to allow the LibOS to bind to resources [1]
* Allows the separation of protection and resource use [1]
* only checks authorization during bind time [1]
** Application's with complex needs for resources only authorized during bind.[1]
* access checking is done during access time and there is no need to understand complex resources needs during access[1]
** (this means that the exokernel checks once to make sure an application has authorization once approved, when the application tries to use the resource the exokernel is only concerned about policy conflict's)--[[User:Asoknack|Asoknack]] 18:20, 9 October 2010 (UTC)
** allows the kernel to protect the resources with out understanding what the resource is [1]
*three way's to implement
* Hardware Mechanisms [1]
* Software caching [1]
* Downloading application code [1]
''' Downloading Code to the Kernel '''
* used to implement secure bindings , and improve performance[1]
** eliminate the number of kernel crossings [1]
** downloaded code can be run with out the application to be scheduled [2]
==== Visible Resource Revocation ====
* Used for most resources [1]
** allows for LibOS to help with deallocation [1]
** LibOS are able to garner what resources are scare [1]
* Slower than Invisible as application involvement is required [1]
** ex of when invisible is used is Processor addressing-context identifiers [1]
==== Abort Protocol ====
* allows the exokernel to take resources away from the LibOS [1]
* used when the LibOS fails to respond to the revocation request [1]
* Exokernel must be careful not to delete as the LibOS might need to write some system critical data to the resource [1]

== Comparisons ==
====Exokernel/Microkernel====
'''Similarities'''
* Limited functionality in kernel
** functionality in kernel to handle sharing of resources and security
** avoids programming directly to hardware which creates a dependency
* Additional functionality provided in user space as processes
'''Differences'''
* Minimal abstractions provided by the kernel
** Applications given more power in exokernel

====Exokernel/VM====
'''Similarities'''
* Idea of partitioning resources between applications/OSs
* "Control" of resource given
* Isolation from other applications/OSs
'''Differences'''
* Exokernel runs applications, VM runs OS
* VM uses a hostOS and guestOSs run on top
* Virtualization on VMs, Exokernel deals with real resources
* VM hides a lot of information because it emulates. Exokernel does not.

====Microkernel/VM====
'''Differences'''
* With a virtual machine, you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System.
* This can be costly but the benefits are that it's easier and all the standard OS features are available.

== References ==
[1]<nowiki> Engler, D. R., Kaashoek, M. F., and O'Toole, J. 1995. Exokernel: an operating system architecture for application-level resource management. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 251-266. DOI= http://doi.acm.org/10.1145/224056.224076 </nowiki>

[2]<nowiki>Engler, Dawson R. "The Exokernel Operating System Architecture." Diss. Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998. Web. 9 Oct. 2010. <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.61.5054&rep=rep1&type=pdf>.</nowiki>

[3]<nowiki>Kaashoek, M. F., Engler, D. R., Ganger, G. R., Briceño, H. M., Hunt, R., Mazières, D., Pinckney, T., Grimm, R., Jannotti, J., and Mackenzie, K. 1997. Application performance and flexibility on exokernel systems. In Proceedings of the Sixteenth ACM Symposium on Operating Systems Principles (Saint Malo, France, October 05 - 08, 1997). W. M. Waite, Ed. SOSP '97. ACM, New York, NY, 52-65. DOI= http://doi.acm.org/10.1145/268998.266644 </nowiki>

[4]<nowiki>Vallee, G.; Naughton, T.; Engelmann, C.; Hong Ong; Scott, S.L.; , "System-Level Virtualization for High Performance Computing," Parallel, Distributed and Network-Based Processing, 2008. PDP 2008. 16th Euromicro Conference on , vol., no., pp.636-643, 13-15 Feb. 2008
DOI= http://doi.acm.org/10.1109/PDP.2008.85 </nowiki>

[5]<nowiki>Goldberg, R. P. 1973. Architecture of virtual machines. In Proceedings of the Workshop on Virtual Computer Systems (Cambridge, Massachusetts, United States, March 26 - 27, 1973). ACM, New York, NY, 74-112. DOI= http://doi.acm.org/10.1145/800122.803950 </nowiki>

[6]<nowiki>Vallee, G., Naughton, T., and Scott, S. L. 2007. System management software for virtual environments. In Proceedings of the 4th international Conference on Computing Frontiers (Ischia, Italy, May 07 - 09, 2007). CF '07. ACM, New York, NY, 153-160. DOI= http://doi.acm.org/10.1145/1242531.1242555 </nowiki>

[7]<nowiki>Liedtke, J. 1995. On micro-kernel construction. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 237-250. DOI= http://doi.acm.org/10.1145/224056.224075 </nowiki>

[8]<nowiki>Microkernel verses monolithic kernel
http://www.vmars.tuwien.ac.at/courses/akti12/journal/04ss/article_04ss_Roch.pdf - Roch</nowiki>

I will site it/reference it better later

== Unsorted ==
An overview of exokernels,virtual machines, microkernels *[http://www2.supchurch.org:10999/files/school/classes/CSCI4730/Lectures/grad-structures.ppt Overview](Power Point) 
Should not be used as a source but an overview.

The original paper on [http://portal.acm.org/citation.cfm?id=224076 Exokernels] --[[User:Gautam|Gautam]] 22:39, 6 October 2010 (UTC)

Exokernel-
Minimalistic abstractions for developers
Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs.
Exokernel – fewest hardware abstractions to developer
Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system
Virtual machine is a simulation of any or devices requested by an application program
Exokenel – I’ve got a sound card
Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match
Microkernel – I’ve got sound card that plays Khazikstan sound format only
MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below
-Rovic

Outlining some main features here as I see them.

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have.

I'll locate some references later on. --[[User:Slay|Slay]] 15:00, 7 October 2010 (UTC)

I'm just going to post my answer for question 1 on the individuel assignment and hope it helps. --[[User:Aellebla|Aellebla]] 15:06, 12 October 2010 (UTC)

The design of the micro kernel was to take everything they could out of the Kernel and put it into a process. For ex, networking would be put into a process instead of staying in the kernel. The micro kernel dev's tried to keep lots of things in user space for efficiency. But one major problem with this is there would be a large amount of moving from a process to the kernel to user space and back again and this is a costly, non efficient process.It was an application specific OS, there was no multiplexing. With a virtual machine you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System. This is very heavy however but the benefits are that it‟s easy and all the standard OS features are there whereas in a microkernel setup they would not all be there and this can be seen as a compromise.

Exokernels can be seen as a compromise to virtual machines and microkernels because virtual machines emulate and exokernels do not. When you emulate something you hide a lot of the actual information because you wouldn‟t be able to see the „real‟ hardware. If we look at a virtual box setup running Linux, and we go look at all the hardware, it will be displayed as fake hardware.

Maybe we can have an introduction - paragraph or so on each type - then similarities - differences - and the compromise. I am going to do some research and writing this weekend and I will put some up -- Jslonosky

btw in my page (i guess you can call it that) i have some resources i have found --[[User:Asoknack|Asoknack]] 15:50, 8 October 2010 (UTC)
- Wow, nice man. I will go ahead and write up the descriptive paragraphs on each kernel and virtual machine if no one minds. --Jslonosky

I think we should divide up the paragraphs and proofread each others instead. (Are there only 4 of us?) I don't have much time to work on this today though but I'll try to work on it tomorrow morning. - Slay

Sure guy. That sounds good. There should be 5 or 6 of us though.. . Oh well. Their loss. I will do some before or after work today. Ill start with Microkernel since there is not a large amount of info here, and so we don't overlap each other - JSlonosky

yeah i think there was more like 7 of us btw if any one has any more information feel free to add it would be nice if you add the references so that way citing is really easy on acm.org it will auto give you the citation info (where it says Display Formats click on ACM Ref and new window with the citation info auto pop's up) --[[User:Asoknack|Asoknack]] 02:28, 11 October 2010 (UTC)

I added an outline of the similarities and differences. Add any more that I missed. These are from observations so I don't have any resources. -Slay
That's probably fine. Our textbook probably outlines some of them, so I am sure we can find a few there - JSlonosky

Talked to the teacher today and for VM he said we should focus on the implementation such as Xen and VMware , he also said to talk about para virtualization --[[User:Asoknack|Asoknack]] 18:42, 12 October 2010 (UTC)

A paper about emulation and paravirtualization [http://portal.acm.org/citation.cfm?id=1189289&coll=GUIDE&dl=GUIDE&CFID=105648137&CFTOKEN=47153176&ret=1#Fulltext link] - Slay

Oh no big words. Sorry about the Microkernels not done yet. Working on an outline now. Finally found how to access the ACM through carleton. Gawd.
I am planning an outline, quick bit about kernels in general, (maybe mention monolith kernels?), and what microkernels do.
I see the microkernel outline info and a reference ( Whomever did that == hero: true) about the scheduling and the Memory management. Should that be included in kernels in general and then mention what microkernels build upon/change? - JSlonosky

Sorry late to the party here. My mistake was not checking the discussion page when I checked in. I don't want to trample anyone's current work but I don't see any work on the final essay done. I would love to help just need to know where I can step in so as to not screw anyone else up. -- [[User:Cling|Cling]]

I don't think I'll be able to write up something for the final essay, even though I suggested splitting it. I'll do research tonight though on the paravirtualization. If I find the time, I'll try to write something. Sorry about that. --[[User:Slay|Slay]] 21:52, 13 October 2010 (UTC)

We all have 3004 to do too, man. I do not think anyone has chosen to do Virtual Machine section yet, or the Exokernel itself. But the contrast paragraph and the intro is chosen, and intro is done. Microkernel and kernel will be done in a hour I hope. -- JSlonosky

I can attempt to write up anything, the issue is I don't have any context on what to write, how do I tie it in to the rest of the essay? I only have a Japanese Quiz tomorrow morning then I should be good to write anything up for the rest of the day. As someone who has already written part of the essay, and assuming I attempt the exokernel section, how much do you think I should write? Should it just be about exokernel or should there be comparisons to the other topics? Thanks --[[User:Cling|Cling]] 23:14, 13 October 2010 (UTC)

Go with the Exokernel itself. Slade is getting off work in a hour and we can double check what he is doing then. We can put it together tomorrow sometime, and fill in the other stuff. - JSLonosky

I'll attempt to work on VM tonight, then. I would feel so bad if I didn't write anything. -Slay

Still wondering how much to write, I think we should decide on a decent word count or length so we don't have one short section (which would probably be mine) and/or one massive section that dwarfs all the others. If anyone has already written a section could you post your word count so we can aim to be around there, it would obviously be just a recommendation but it's just better to be on the safe side and have everything uniform. I haven't seen any formal requirements for the essay but I could be wrong, I also haven't been to class in a while. --[[User:Cling|Cling]] 23:33, 13 October 2010 (UTC)

Yeah Slay, VM probably doesnt have much to write about. Get something down, and we can go over it. CLing, Just write what you think. There is not a lot to go over if I write kernel/microkernel well enough. What is a exokernel? exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction, basically (As said by Slade). I will probably end up with 500 or a bit more words. -- JSlonosky

Sound off!

Who's actually reading this? Add your name to the list...

Rovic P.
Jon Slonosky
Corey Ling
Steph Lay

== The Essay ==

Let's actually breakdown the essay into components then write it here.

I'd like to go along the premise that microkernels and and virtual machines are "weaker" than exokernels in design for the essay. If anyone has any objections, add it here.

-Slade

what do you mean by "weaker"(i think you mean exokernels' takes the best of both worlds ) --[[User:Asoknack|Asoknack]] 02:45, 13 October 2010 (UTC)

What I mean by weaker is that we should focus on the things microkernels and virtual machines may not do as well compared to a system based off an exokernel design and then focus on how an exokenenel can take the best of both worlds. Please choose which section you will work on, that's not to say it'll be the only part you do, but rather we'll all contribute to each part please. 1 day left.
-Slade

...to the extent that exokernels be seen as a compromise between virtual machines and microkernels.
-I'll work on the initial intro. -Slade

3 paragraphs that prove it
Explain how the key design characteristics of these three system architectures compare with each other.

intro/thesis statement -Rovic P.

In Computer Science, the kernel is the component at the center of the majority of operating systems. The kernel is a bridge for applications to access the hardware level. It is responsible for managing the system's resources such as memory, disk storage, task management and networking. It is how the kernel goes about such management and its connections that we are comparing Exokernels to Microkernels and Virtual Machines. In the Exokernel conceptual model, we can see exokernels become much smaller than microkernels since by design, they are tiny and strive to keep functionality limited to protection and multiplexing of resources. The Virtual Machine Implementation of virtualizing all devices on the system may provide compatibility, but it adds a layer of complexity within the system less efficient than a real machine as it accesses the hardware indirectly. It can be observed how the exokernel provides low level hardware access and provide custom abstraction to those devices to improve program performance as opposed to a VM's implementation. The exokernel concept has a design that can take the better concepts of microkernels and virtual machines to the extend that exokernels can be seen as a compromise between a virtual machine and a microkernel.

Paragraph 1 -Microkernel -Jon S.

The kernel is the most important part of an operating system. Without the kernel, an operating system could not function.

A kernel is the lowest level section of an operating system. It has the most privileges of the system. It runs along side of the ‘user space’. It is in the ‘user space’ where a user has access and where the user can run its applications and libraries.[8] This leaves the kernel with the need to manage the other necessary processes such as the File Systems and the process scheduling. The kernel is layered with the most authoritative process on its lowest level.[8] A monolithic kernel, a kernel that contains all mandatory processes within itself, was the common kernel type of the earlier versions of today’s operating systems utilized. However, this architecture had problems. [8] If the kernel needed to be updated with more code, or a fix for the system, the entire kernel would need to be compiled, and due to the amount of processes within it, it would take an inefficient amount of time. This is where a microkernel becomes practical.

The concept of a microkernel is reduce the code within the kernel, and it is only included in the kernel if it would affect the system in any way, for example for performance and efficiency reasons. [7] So, a microkernel is a kernel that has a reduced amount of mandatory software within itself. This means that it contains less software that it has to manage, and has a reduced size. A microkernel that emerged at the end of the 1980’s to the early 1990’s has the structure that processes like the File Systems and the Drivers are removed from it, leaving the kernel with process control and input/out control, and interrupts. [8] This new structure makes the system much more modular, and easier to provide solutions. If a driver must be patched or upgraded, the kernel does not need to be recompiled. [7] The old driver can be removed, and while the device waits for the system to recognize it, the operating system replaces the driver. This lets real-time updating, and it can be done while the computer is still functional. This can reduce the complete crash of the system. If a device fails, the kernel will not crash itself, like a monolithic kernel would. The microkernel can reload the driver of the device that failed and continue functioning. [7]

Want more on the scheduling? I can do that if wanted.

Paragraph 2 -Virtual Machine -Steph L.

A Virtual Machine, or VM, is a software abstraction of a physical machine. This entails virtualization of the physical machines resources in order to share them among OS run in the VM. Virtualizing these resources allow the OS to run as if it were on a full machine when, in reality, it is actually running in a virtualized environment on top of a hostOS, the OS actually running on the machine, sharing the resources.

Virtual Machines generally contain two key components, the Virtual Machine Monitor, or VMM and the VM.

The VMM, also known as the hypervisor, manages the virtualization of the physical resources and the interactions with the VM running on top. In other words, it mediates between the virtualized world and the physical world, keeping them separate and monitoring their interactions with each other. The hypervisor is what allows the VM to operate as if it were on its own machine by handling any requests to resources and maintaining these requests with what has actually been provided to the VM by the hostOS. The hostOS is provides management for the VMM as well as physical access to devices, hardware and drivers.

The VM is what contains the OS we are running through virtualization. This OS is called the guestOS and it will only be able to access any resources that have been made available to the VM by the hostOS. Otherwise, the guestOS will not know about any other resources and does not have direct access to physical hardware. This will be taken care of by the VMM.

[ I'll need to do some more research on the types of virtualization though before I can discuss that. If anyone has more information on them to put up in the points that would be helpful but I'll get to it right after class tomorrow morning. ]

Paragraph 3 -Exokernel -Corey L

Paragraph 4 - Contrast/Compromise --[[User:Asoknack|Asoknack]]

Conclusion - Jon S. - Only a sentence per paragraph, excluding Intro

Sweet. Looks like we got it covered. We should read each others parts and put suggestions and edits. One of us should try and change it to one style if there are contradictions. And to put it on the main page. We can figure that out tomorrow. - Jon S

Once the other parts are up and you see anything you know of as a good reference to back it up, put the link so we can use it. -Slade

Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-14T04:23:36Z

Slay: /* The Essay */

== Microkernel ==
* Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
* Keep basic functionality in kernel to handle sharing of resources
* Separation allows for manageability and security, corruption in one does not necessarily cause failure in system
* Large amount of moving from a process to Kernel to user space and back again, this is a costly operation.

----

''' Microkernel '''
* try's to minimize the amount of software that is mandatory or required [7]
advantages of Microkernel
* favors a modular system structure [7]
* one failure of a program does not impact any other programs [7]
* can support more than one api or strategies since all programs are separated [7]
==== Microkernel Concepts ====
* piece of code is allowed in the kernel only if moving it outside the kernel would adversely affect the system. [7]
* any subsystem program created must be independent of all other subsystem's, any subsystem that is used can guarantee this from all other subsystems [7]
===== Address Space =====
* a mapping that relates the physical page to the virtual page. [7]
* processor specific [7]
* hide's the hardware's concept of address space [7]
* based off the idea of recursion each subsystem has it's own address space [7]
* the micro kernel provides 3 operations [7]
** Grant [7]
*** allows the owner to give a page to a recipient, provided the recipient want's it the page is removed from the owner's address space and but in the recipients. [7]
*** must be available to the owner. [7]
** Map [7]
*** allows the user to share a page with a recipient [7]
*** page is not removed from the owner's address space. [7]
** Flush [7]
*** remove's the page from all recipients address space [7]
*** how does this work with Grant --[[User:Asoknack|Asoknack]] 19:10, 12 October 2010 (UTC)
* allows memory management and paging out side the kernel
* Map and flush is required for memory manger's and pagers [7]
* can be used to implement access right's [7]
* controlling I/O Right's and driver's are not done at kernel level [7]

===== Thread's IPC =====
* Threads
** in the kernel [7]
** Since a thread has an address space , all changes to the thread need to be done by the kernel [7]
* IPC [7]
** in the kernel IPC
** grant and map also need IPC (So buye the priciple above this has to be in the kernel)[7]
** basic way for sub process to communicate. [7]
* Interrupts
** partially in the kernel [7]
** hard ware is a set of thread's which are empty except for there unique sender id [7]
** transformation of the message to the interrupt is done in the kernel [7]
** the kernel is not involved in device - specific interrupt's and does not understand the interrupt. [7]
*** resting the interrupt is done at user level [7]
** if a privileged command is need it is done implicitly the next time an IPC command is sent from the device [7]

===== Unique Identifiers =====

== Virtual Machine ==
* Partitioning or virtualizing resources among OS virtualization running on top of host OS
* Virtualized OS believe running on full machine on its own

----
System Level Virtualization

=== VMM ===
* stands for Virtual Machine Monitor, also known as the hyper-visor[4]
* responsible for virtualization of hardware(mapping physical to virtual) and the VM that run on top of the virtuallized hardware [4]
* usually a small os with no drivers , so it is coupled with a linux distro that provides device / hardware access [4]
** the os that the VMM is using for driver's is called the hostOS [6]
*the hostOS provides login and physical access to the hardware as well as management for the VMM [6]
=== VM ===
* the OS that the vm is running is called the guestOS [6]
* the guestOS only sees resources that have been allocated to the VM [6]
==== three approaches ====
*Type I virtualization [5]
** runs off the physical hardware [4]
** Isolation of the guestOs from the hardware is done threw processe level protection meachnism[6]
*** ring 0 = VMM [6]
*** ring 1 = VM [6]
*** this means all instructions from the VM must go threw the VMM [6]
** since there can be multiple VM's on a computer the scheduling is done by the VMM [6]
** on boot the VMM creates a hardware platform for the VM [6]
** load's the VM kernel into virtual memory and then boot's it like a regular computer [6]
** ex. Xen [4]
*Type II virtualization [5]
** run off the host Os [4]
** ex. VMware , QEMU [4]
* Para-virtualization [6]
** Similar to Type but use the HostOs for Device driver access [6]
** Provide a virtualization that is similar to hardware [From the paper posted, no citation yet]
** GuestOS and Hypervisor work together to improve performance

== Exokernel ==
* Micro-kernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
* Less functionality provided by kernel, security and handling of resource sharing
* Once application receives resource, it can use it as it wishes/in control
* Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware

----
* multiplex resources securely providing protection to mutual distrustful application threw the use of secure binding's[1]
* Goal of the exokernel is to give LibOS maximum freedom with out allowing them to interfere with each other. to do this the exokernel separates protection from management in doing this it provide 3 important tasks[1]
** tracking ownership of resources [1]
** ensuring protection by guarding all resource usage and binding points (not to shure what binding points are)[1]
** revoking access to the resources [1]
* LibrayOS (LibOs)
** Reduces the number of kernel crossings[1]
** Not trusted by the exokernel so can be trusted by the application , Example given is a bad parameter passed to the LibOs only the application is affected.[1] (So LibOs cant interact with kernel ???)
** Any application running on the Exokernel can change the LibrayOs freely [1]
** Application that use LibOS that implement standard interfaces (POSIX) will be portable on any system with the same interface [1]
** LibOs can be made portable if it is designed to interact with a low-level machine independent level to hide hardware details [1]

=== Exokernel Design ===
==== Design Principles ====
*Securely Expose Hardware [1]
** an Exokernel tries to create low level primitives that the hardware resources can be accessed from, this also includes interrupts,exceptions [1]
** the exokernel also export privileged instructions to the LibOS so that traditional OS abstractions can be implemented (eg Process , address pace)[1]
** Exokernels should avoid resource management except when required protection ( allocation , revocation , ownership)[1]
** application based resource management is the best way to build flexible efficient flexible systems [1]
*Expose allocation[1]
** allow LibOs to request physical resources [1]
** resource allocation should not be automatic, the LibOS should participate in every single allocation decision [1]
*Expose Names[1]
** Use physical name's when ever possible[3] (not to sure what physical names are, I think it is as simple as what the hardware is called)--[[User:Asoknack|Asoknack]] 20:27, 9 October 2010 (UTC)
** Physical names capture useful information [3]
*** safer than and less resource intensive than virtual names as no translations are needed[3]
*Expose Revocation [1]
** use visible revocation protocol [1]
** allows well behaved LibOS to preform application level resource management [1]
** Visible revocation allows the LibOS to choose what instance of the resource to release[1](Visible means that when revocation happens the exokernel tell the LibOS that resource is being revoked)
''' Policy '''
* LibOS handle resource policy decisions
* Exokernels have a policy to decided between competing LibOS (Priority , share of resources)
** it enforces this threw allocation and deallocation (every thing can achieved threw this even what block to write and such)

==== Secure Bindings ====
* Used by the exokernel to allow the LibOS to bind to resources [1]
* Allows the separation of protection and resource use [1]
* only checks authorization during bind time [1]
** Application's with complex needs for resources only authorized during bind.[1]
* access checking is done during access time and there is no need to understand complex resources needs during access[1]
** (this means that the exokernel checks once to make sure an application has authorization once approved, when the application tries to use the resource the exokernel is only concerned about policy conflict's)--[[User:Asoknack|Asoknack]] 18:20, 9 October 2010 (UTC)
** allows the kernel to protect the resources with out understanding what the resource is [1]
*three way's to implement
* Hardware Mechanisms [1]
* Software caching [1]
* Downloading application code [1]
''' Downloading Code to the Kernel '''
* used to implement secure bindings , and improve performance[1]
** eliminate the number of kernel crossings [1]
** downloaded code can be run with out the application to be scheduled [2]
==== Visible Resource Revocation ====
* Used for most resources [1]
** allows for LibOS to help with deallocation [1]
** LibOS are able to garner what resources are scare [1]
* Slower than Invisible as application involvement is required [1]
** ex of when invisible is used is Processor addressing-context identifiers [1]
==== Abort Protocol ====
* allows the exokernel to take resources away from the LibOS [1]
* used when the LibOS fails to respond to the revocation request [1]
* Exokernel must be careful not to delete as the LibOS might need to write some system critical data to the resource [1]

== Comparisons ==
====Exokernel/Microkernel====
'''Similarities'''
* Limited functionality in kernel
** functionality in kernel to handle sharing of resources and security
** avoids programming directly to hardware which creates a dependency
* Additional functionality provided in user space as processes
'''Differences'''
* Minimal abstractions provided by the kernel
** Applications given more power in exokernel

====Exokernel/VM====
'''Similarities'''
* Idea of partitioning resources between applications/OSs
* "Control" of resource given
* Isolation from other applications/OSs
'''Differences'''
* Exokernel runs applications, VM runs OS
* VM uses a hostOS and guestOSs run on top
* Virtualization on VMs, Exokernel deals with real resources
* VM hides a lot of information because it emulates. Exokernel does not.

====Microkernel/VM====
'''Differences'''
* With a virtual machine, you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System.
* This can be costly but the benefits are that it's easier and all the standard OS features are available.

== References ==
[1]<nowiki> Engler, D. R., Kaashoek, M. F., and O'Toole, J. 1995. Exokernel: an operating system architecture for application-level resource management. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 251-266. DOI= http://doi.acm.org/10.1145/224056.224076 </nowiki>

[2]<nowiki>Engler, Dawson R. "The Exokernel Operating System Architecture." Diss. Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998. Web. 9 Oct. 2010. <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.61.5054&rep=rep1&type=pdf>.</nowiki>

[3]<nowiki>Kaashoek, M. F., Engler, D. R., Ganger, G. R., Briceño, H. M., Hunt, R., Mazières, D., Pinckney, T., Grimm, R., Jannotti, J., and Mackenzie, K. 1997. Application performance and flexibility on exokernel systems. In Proceedings of the Sixteenth ACM Symposium on Operating Systems Principles (Saint Malo, France, October 05 - 08, 1997). W. M. Waite, Ed. SOSP '97. ACM, New York, NY, 52-65. DOI= http://doi.acm.org/10.1145/268998.266644 </nowiki>

[4]<nowiki>Vallee, G.; Naughton, T.; Engelmann, C.; Hong Ong; Scott, S.L.; , "System-Level Virtualization for High Performance Computing," Parallel, Distributed and Network-Based Processing, 2008. PDP 2008. 16th Euromicro Conference on , vol., no., pp.636-643, 13-15 Feb. 2008
DOI= http://doi.acm.org/10.1109/PDP.2008.85 </nowiki>

[5]<nowiki>Goldberg, R. P. 1973. Architecture of virtual machines. In Proceedings of the Workshop on Virtual Computer Systems (Cambridge, Massachusetts, United States, March 26 - 27, 1973). ACM, New York, NY, 74-112. DOI= http://doi.acm.org/10.1145/800122.803950 </nowiki>

[6]<nowiki>Vallee, G., Naughton, T., and Scott, S. L. 2007. System management software for virtual environments. In Proceedings of the 4th international Conference on Computing Frontiers (Ischia, Italy, May 07 - 09, 2007). CF '07. ACM, New York, NY, 153-160. DOI= http://doi.acm.org/10.1145/1242531.1242555 </nowiki>

[7]<nowiki>Liedtke, J. 1995. On micro-kernel construction. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles (Copper Mountain, Colorado, United States, December 03 - 06, 1995). M. B. Jones, Ed. SOSP '95. ACM, New York, NY, 237-250. DOI= http://doi.acm.org/10.1145/224056.224075 </nowiki>

[8]<nowiki>Microkernel verses monolithic kernel
http://www.vmars.tuwien.ac.at/courses/akti12/journal/04ss/article_04ss_Roch.pdf - Roch</nowiki>

I will site it/reference it better later

== Unsorted ==
An overview of exokernels,virtual machines, microkernels *[http://www2.supchurch.org:10999/files/school/classes/CSCI4730/Lectures/grad-structures.ppt Overview](Power Point) 
Should not be used as a source but an overview.

The original paper on [http://portal.acm.org/citation.cfm?id=224076 Exokernels] --[[User:Gautam|Gautam]] 22:39, 6 October 2010 (UTC)

Exokernel-
Minimalistic abstractions for developers
Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs.
Exokernel – fewest hardware abstractions to developer
Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system
Virtual machine is a simulation of any or devices requested by an application program
Exokenel – I’ve got a sound card
Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match
Microkernel – I’ve got sound card that plays Khazikstan sound format only
MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below
-Rovic

Outlining some main features here as I see them.

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have.

I'll locate some references later on. --[[User:Slay|Slay]] 15:00, 7 October 2010 (UTC)

I'm just going to post my answer for question 1 on the individuel assignment and hope it helps. --[[User:Aellebla|Aellebla]] 15:06, 12 October 2010 (UTC)

The design of the micro kernel was to take everything they could out of the Kernel and put it into a process. For ex, networking would be put into a process instead of staying in the kernel. The micro kernel dev's tried to keep lots of things in user space for efficiency. But one major problem with this is there would be a large amount of moving from a process to the kernel to user space and back again and this is a costly, non efficient process.It was an application specific OS, there was no multiplexing. With a virtual machine you are not virtualizing apps like with a microkernel but virtualizing an entire Operating System. This is very heavy however but the benefits are that it‟s easy and all the standard OS features are there whereas in a microkernel setup they would not all be there and this can be seen as a compromise.

Exokernels can be seen as a compromise to virtual machines and microkernels because virtual machines emulate and exokernels do not. When you emulate something you hide a lot of the actual information because you wouldn‟t be able to see the „real‟ hardware. If we look at a virtual box setup running Linux, and we go look at all the hardware, it will be displayed as fake hardware.

Maybe we can have an introduction - paragraph or so on each type - then similarities - differences - and the compromise. I am going to do some research and writing this weekend and I will put some up -- Jslonosky

btw in my page (i guess you can call it that) i have some resources i have found --[[User:Asoknack|Asoknack]] 15:50, 8 October 2010 (UTC)
- Wow, nice man. I will go ahead and write up the descriptive paragraphs on each kernel and virtual machine if no one minds. --Jslonosky

I think we should divide up the paragraphs and proofread each others instead. (Are there only 4 of us?) I don't have much time to work on this today though but I'll try to work on it tomorrow morning. - Slay

Sure guy. That sounds good. There should be 5 or 6 of us though.. . Oh well. Their loss. I will do some before or after work today. Ill start with Microkernel since there is not a large amount of info here, and so we don't overlap each other - JSlonosky

yeah i think there was more like 7 of us btw if any one has any more information feel free to add it would be nice if you add the references so that way citing is really easy on acm.org it will auto give you the citation info (where it says Display Formats click on ACM Ref and new window with the citation info auto pop's up) --[[User:Asoknack|Asoknack]] 02:28, 11 October 2010 (UTC)

I added an outline of the similarities and differences. Add any more that I missed. These are from observations so I don't have any resources. -Slay
That's probably fine. Our textbook probably outlines some of them, so I am sure we can find a few there - JSlonosky

Talked to the teacher today and for VM he said we should focus on the implementation such as Xen and VMware , he also said to talk about para virtualization --[[User:Asoknack|Asoknack]] 18:42, 12 October 2010 (UTC)

A paper about emulation and paravirtualization [http://portal.acm.org/citation.cfm?id=1189289&coll=GUIDE&dl=GUIDE&CFID=105648137&CFTOKEN=47153176&ret=1#Fulltext link] - Slay

Oh no big words. Sorry about the Microkernels not done yet. Working on an outline now. Finally found how to access the ACM through carleton. Gawd.
I am planning an outline, quick bit about kernels in general, (maybe mention monolith kernels?), and what microkernels do.
I see the microkernel outline info and a reference ( Whomever did that == hero: true) about the scheduling and the Memory management. Should that be included in kernels in general and then mention what microkernels build upon/change? - JSlonosky

Sorry late to the party here. My mistake was not checking the discussion page when I checked in. I don't want to trample anyone's current work but I don't see any work on the final essay done. I would love to help just need to know where I can step in so as to not screw anyone else up. -- [[User:Cling|Cling]]

I don't think I'll be able to write up something for the final essay, even though I suggested splitting it. I'll do research tonight though on the paravirtualization. If I find the time, I'll try to write something. Sorry about that. --[[User:Slay|Slay]] 21:52, 13 October 2010 (UTC)

We all have 3004 to do too, man. I do not think anyone has chosen to do Virtual Machine section yet, or the Exokernel itself. But the contrast paragraph and the intro is chosen, and intro is done. Microkernel and kernel will be done in a hour I hope. -- JSlonosky

I can attempt to write up anything, the issue is I don't have any context on what to write, how do I tie it in to the rest of the essay? I only have a Japanese Quiz tomorrow morning then I should be good to write anything up for the rest of the day. As someone who has already written part of the essay, and assuming I attempt the exokernel section, how much do you think I should write? Should it just be about exokernel or should there be comparisons to the other topics? Thanks --[[User:Cling|Cling]] 23:14, 13 October 2010 (UTC)

Go with the Exokernel itself. Slade is getting off work in a hour and we can double check what he is doing then. We can put it together tomorrow sometime, and fill in the other stuff. - JSLonosky

I'll attempt to work on VM tonight, then. I would feel so bad if I didn't write anything. -Slay

Still wondering how much to write, I think we should decide on a decent word count or length so we don't have one short section (which would probably be mine) and/or one massive section that dwarfs all the others. If anyone has already written a section could you post your word count so we can aim to be around there, it would obviously be just a recommendation but it's just better to be on the safe side and have everything uniform. I haven't seen any formal requirements for the essay but I could be wrong, I also haven't been to class in a while. --[[User:Cling|Cling]] 23:33, 13 October 2010 (UTC)

Yeah Slay, VM probably doesnt have much to write about. Get something down, and we can go over it. CLing, Just write what you think. There is not a lot to go over if I write kernel/microkernel well enough. What is a exokernel? exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction, basically (As said by Slade). I will probably end up with 500 or a bit more words. -- JSlonosky

Sound off!

Who's actually reading this? Add your name to the list...

Rovic P.
Jon Slonosky
Corey Ling
Steph Lay

== The Essay ==

Let's actually breakdown the essay into components then write it here.

I'd like to go along the premise that microkernels and and virtual machines are "weaker" than exokernels in design for the essay. If anyone has any objections, add it here.

-Slade

what do you mean by "weaker"(i think you mean exokernels' takes the best of both worlds ) --[[User:Asoknack|Asoknack]] 02:45, 13 October 2010 (UTC)

What I mean by weaker is that we should focus on the things microkernels and virtual machines may not do as well compared to a system based off an exokernel design and then focus on how an exokenenel can take the best of both worlds. Please choose which section you will work on, that's not to say it'll be the only part you do, but rather we'll all contribute to each part please. 1 day left.
-Slade

...to the extent that exokernels be seen as a compromise between virtual machines and microkernels.
-I'll work on the initial intro. -Slade

3 paragraphs that prove it
Explain how the key design characteristics of these three system architectures compare with each other.

intro/thesis statement -Rovic P.

In Computer Science, the kernel is the component at the center of the majority of operating systems. The kernel is a bridge for applications to access the hardware level. It is responsible for managing the system's resources such as memory, disk storage, task management and networking. It is how the kernel goes about such management and its connections that we are comparing Exokernels to Microkernels and Virtual Machines. In the Exokernel conceptual model, we can see exokernels become much smaller than microkernels since by design, they are tiny and strive to keep functionality limited to protection and multiplexing of resources. The Virtual Machine Implementation of virtualizing all devices on the system may provide compatibility, but it adds a layer of complexity within the system less efficient than a real machine as it accesses the hardware indirectly. It can be observed how the exokernel provides low level hardware access and provide custom abstraction to those devices to improve program performance as opposed to a VM's implementation. The exokernel concept has a design that can take the better concepts of microkernels and virtual machines to the extend that exokernels can be seen as a compromise between a virtual machine and a microkernel.

Paragraph 1 -Microkernel -Jon S.

The kernel is the most important part of an operating system. Without the kernel, an operating system could not function.

A kernel is the lowest level section of an operating system. It has the most privileges of the system. It runs along side of the ‘user space’. It is in the ‘user space’ where a user has access and where the user can run its applications and libraries.[8] This leaves the kernel with the need to manage the other necessary processes such as the File Systems and the process scheduling. The kernel is layered with the most authoritative process on its lowest level.[8] A monolithic kernel, a kernel that contains all mandatory processes within itself, was the common kernel type of the earlier versions of today’s operating systems utilized. However, this architecture had problems. [8] If the kernel needed to be updated with more code, or a fix for the system, the entire kernel would need to be compiled, and due to the amount of processes within it, it would take an inefficient amount of time. This is where a microkernel becomes practical.

The concept of a microkernel is reduce the code within the kernel, and it is only included in the kernel if it would affect the system in any way, for example for performance and efficiency reasons. [7] So, a microkernel is a kernel that has a reduced amount of mandatory software within itself. This means that it contains less software that it has to manage, and has a reduced size. A microkernel that emerged at the end of the 1980’s to the early 1990’s has the structure that processes like the File Systems and the Drivers are removed from it, leaving the kernel with process control and input/out control, and interrupts. [8] This new structure makes the system much more modular, and easier to provide solutions. If a driver must be patched or upgraded, the kernel does not need to be recompiled. [7] The old driver can be removed, and while the device waits for the system to recognize it, the operating system replaces the driver. This lets real-time updating, and it can be done while the computer is still functional. This can reduce the complete crash of the system. If a device fails, the kernel will not crash itself, like a monolithic kernel would. The microkernel can reload the driver of the device that failed and continue functioning. [7]

Want more on the scheduling? I can do that if wanted.

Paragraph 2 -Virtual Machine -Steph L.

A Virtual Machine, or VM, is a software abstraction of a physical machine. This entails virtualization of the physical machines resources in order to share them among operating systems, or OS, run in the VM. Virtualizing these resources allow the OS to run as if it were on a full machine when, in reality, it is actually running in a virtualized environment on top of a hostOS, the OS actually running on the machine, sharing the resources.

Virtual Machines generally contain two key components, the Virtual Machine Monitor, or VMM and the VM.

The VMM, also known as the hypervisor, manages the virtualization of the physical resources and the interactions with the VM running on top. In other words, it mediates between the virtualized world and the physical world, keeping them separate and monitoring their interactions with each other. The hypervisor is what allows the VM to operate as if it were on its own machine by handling any requests to resources and maintaining these requests with what has actually been provided to the VM by the hostOS. The hostOS is provides management for the VMM as well as physical access to devices, hardware and drivers.

The VM is what contains the OS we are running through virtualization. This OS is called the guestOS and it will only be able to access any resources that have been made available to the VM by the hostOS. Otherwise, the guestOS will not know about any other resources and does not have direct access to physical hardware. This will be taken care of by the VMM.

[ I'll need to do some more research on the types of virtualization though before I can discuss that. If anyone has more information on them to put up in the points that would be helpful but I'll get to it right after class tomorrow morning. ]

Paragraph 3 -Exokernel -Corey L

Paragraph 4 - Contrast/Compromise --[[User:Asoknack|Asoknack]]

Conclusion - Jon S. - Only a sentence per paragraph, excluding Intro

Sweet. Looks like we got it covered. We should read each others parts and put suggestions and edits. One of us should try and change it to one style if there are contradictions. And to put it on the main page. We can figure that out tomorrow. - Jon S

Once the other parts are up and you see anything you know of as a good reference to back it up, put the link so we can use it. -Slade

Talk:COMP 3000 Essay 1 2010 Question 1

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Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-11T17:37:00Z

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Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-10T16:35:01Z

Slay:

Talk:COMP 3000 Essay 1 2010 Question 2

2010-10-07T15:05:17Z

Slay: Created page with 'Not in this group and I'm not completely sure if this is relevant but I found that UNIX used the POSIX standard while Linux used LSB which is based on the POSIX standard. This a…'

Not in this group and I'm not completely sure if this is relevant but I found that UNIX used the POSIX standard while Linux used LSB which is based on the POSIX standard.
This article outlines some conflicts between them [https://www.opengroup.org/platform/single_unix_specification/uploads/40/13450/POSIX_and_Linux_Application_Compatibility_Final_-_v1.0.pdf]. I didn't find the actual comparisons very comprehensible but the ideas are there. --[[User:Slay|Slay]] 15:05, 7 October 2010 (UTC)

Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-07T15:00:09Z

Slay:

Exokernel-
Minimalistic abstractions for developers
Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs.
Exokernel – fewest hardware abstractions to developer
Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system
Virtual machine is a simulation of any or devices requested by an application program
Exokenel – I’ve got a sound card
Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match
Microkernel – I’ve got sound card that plays Khazikstan sound format only
MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below
-Rovic

Outlining some main features here as I see them.

'''Microkernel'''
- Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
- Keep basic functionality in kernel to handle sharing of resources
- Separation allows for manageability and security, corruption in one does not necessarily cause failure in system

'''Virtual Machine'''
- Partitioning or virtualizing resources among OS virtualization running on top of host OS
- Virtualized OS believe running on full machine on its own

'''Exokernel'''
- Microkernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
- Less functionality provided by kernel, security and handling of resource sharing
- Once application receives resource, it can use it as it wishes/in control
- Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have.

I'll locate some references later on. --[[User:Slay|Slay]] 15:00, 7 October 2010 (UTC)

Talk:COMP 3000 Essay 1 2010 Question 1

2010-10-07T14:58:16Z

Slay:

Exokernel-
Minimalistic abstractions for developers
Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs.
Exokernel – fewest hardware abstractions to developer
Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system
Virtual machine is a simulation of any or devices requested by an application program
Exokenel – I’ve got a sound card
Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match
Microkernel – I’ve got sound card that plays Khazikstan sound format only
MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below
-Rovic

Outlining some main features here as I see them. -Stephany

Microkernel
- Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
- Keep basic functionality in kernel to handle sharing of resources
- Separation allows for manageability and security, corruption in one does not necessarily cause failure in system

Virtual Machine
- Partitioning or virtualizing resources among OS virtualization running on top of host OS
- Virtualized OS believe running on full machine on its own

Exokernel
- Microkernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
- Less functionality provided by kernel, security and handling of resource sharing
- Once application receives resource, it can use it as it wishes/in control
- Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have. -Stephany