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Re: [PATCH] Preheat CPU in benchtests
- From: Andi Kleen <andi at firstfloor dot org>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: libc-alpha at sourceware dot org
- Date: Tue, 23 Apr 2013 07:22:16 -0700
- Subject: Re: [PATCH] Preheat CPU in benchtests
- References: <20130423061028 dot GA6257 at domone dot kolej dot mff dot cuni dot cz>
OndÅej BÃlka <neleai@seznam.cz> writes:
> Benchmarks now are affected by cpu scaling when initialy run at low
> frequency.
>
> Following benchmark runs nonsensial loop first to ensure that benchmark
> are measured at maximal frequency. This greatly cuts time needed to
> get accurate results.
FWIW it's generally safer to disable frequency scaling explicitely
through sysfs (but that needs root), as the reaction time of the
p-state governour can be unpredictable.
On Intel if you run like this too long Turbo may also stop turboing,
as the temperature increases. I typically disable Turbo for micro
benchmarks (set max pstate to be one less)
-Andi
--
ak@linux.intel.com -- Speaking for myself only