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Re: getrusage() problems with user vs. system time reporting

On Mon, Oct 31, 2011 at 09:10:40PM +0000, David Laight wrote:
> The problem is that getting an accurate timestamp is relatively
> expensive. It has been almost the dominant part of process switch.

Let's make this a bit less vague for X86. The numbers are from memory,
but should reflect the order of magnitude. Using TSC or LAPIC for
gettimeofday requires in the order of 100-120 cycles, including system
call overhead. Timer code is roughly half of that. Any other timer,
including HPET and ACPI-fast are above the 1000 cycle barrier and
completely inacceptable.


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