I try to measure the runtime of parts of the Linux kernel code and find that there are two different subsystems for timers. hrtimers means a high resolution timer, and hpet is a timer with high precision.
How is resolution different from accuracy?
http://www.mjmwired.net/kernel/Documentation/timers/
HPET refers to a specific piece of hardware for the x86 platform for the PC (for which Linux has a driver). HPET is described, for example, in this article: http://en.wikipedia.org/wiki/High_Precision_Event_Timer
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