COMP 3000 Essay 2 2010 Question 11
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Background Concepts
In this section we will discuss the fundamentals of timekeeping in real and virtual machines.
Host Timekeeping
This section will provide a brief overview of timekeeping in stand-alone or host PCs/servers.
- todo: add a diagram of a simplified timer showing oscillator, counter, counter input, and interrupt
- todo: explain the parts of the diagram
Counting Strategies
- tick counting
- tickless counting
Timers
- PIT
- CMOS RTC
- Local APIC
- ACPI
- TSC
- HPET
Guest Timekeeping
This section will explain why timing is different for guest operating systems.
Sources of Drift
Discuss what causes the problem in virtual environments. Consider para-virtual and full-virtual architectures.
Impact of Drift
Discuss the impact of error on a few real-world applications.
Compensation Strategies
Discuss common strategies in VM software and in operating systems to compensate for drift. Discuss what happens when the clock is slow and fast.