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Re: [PATCH] Preheat CPU in benchtests
- From: Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>
- To: libc-alpha at sourceware dot org
- Date: Tue, 23 Apr 2013 14:11:41 -0300
- Subject: Re: [PATCH] Preheat CPU in benchtests
- References: <20130423061028 dot GA6257 at domone dot kolej dot mff dot cuni dot cz> <m27gjtwcmf dot fsf at firstfloor dot org> <20130423151725 dot GA16219 at domone dot kolej dot mff dot cuni dot cz>
On 23-04-2013 12:17, OndÅej BÃlka wrote:
> On Tue, Apr 23, 2013 at 07:22:16AM -0700, Andi Kleen wrote:
>> 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.
> Which needs root, so it would request typing password each time you run
> automated benchmarks.
>
> I consider for some time by CPU_CLK_UNHALTED performance counter.
> However a documentation is lacking and I need it with low overhead.
>
I see it should be up to developer to setup the environment and to report
its findings and configuration used. Maybe we might add hooks though
env. vars or additional logic on the Makefile/script that runs the benchmark
(to bind cpu/memory, setup machine scaling, etc.), but I don't think it
should in benchmark logic to setup such things.