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Date: Thu, 18 Nov 2010 14:32:26 +0200
From: Andriy Gapon <avg@freebsd.org>
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To: George Neville-Neil <gnn@neville-neil.com>
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Cc: freebsd-acpi@freebsd.org, freebsd-current@freebsd.org
Subject: Re: aperf/mperf
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on 18/11/2010 05:53 George Neville-Neil said the following:
> 
> On Nov 16, 2010, at 09:37 , Andriy Gapon wrote:
> 
>>
>> Many modern processors provide APERF and MPERF MSRs which allow to easily and
>> reliable calculate average CPU performance level over some interval of time.
>> This also allows to notice things like performance boost, which is generally
>> hidden from software.
>> What would be a proper place to add code that would measure APERF/MPERF ratio?
>> When should trigger such a measurement and over what interval?
>> Ideas?
> 
> Can you point me at documentation for this?   This sounds a lot like
> hwpmc(4) and I wonder if we can make these available in the same way.

Actually it feels more cpufreq-ish to me.
This feature is documented in, e.g., Intel Software Developer's Manual volume 3A,
section 14.2 P-STATE HARDWARE COORDINATION.

-- 
Andriy Gapon