[PATCH] benchtests: Restore the clock_gettime option

Alexander Monakov amonakov@ispras.ru
Tue May 19 21:18:22 GMT 2020



On Tue, 19 May 2020, H.J. Lu via Libc-alpha wrote:

> commit 7621e38bf3c58b2d0359545f1f2898017fd89d05
> Author: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
> Date:   Tue Jan 29 17:43:45 2019 +0000
> 
>     Add generic hp-timing support
> 
> removed the clock_gettime option.  On x86, fewer cycles doesn't
> necessarily mean faster exection due to frequency drop.  We should
> restore the clock_gettime option.

Can you please elaborate more which x86 CPUs you have in mind here,
as since Nehalem (2008) when invariant TSC was introduced, the rdtsc(p)
instructions count at a fixed rate rather than at CPU clock rate.
And before 2008, there were no turbo frequencies and no AVX frequency drop.

Alexander


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