linux-kernel - Re: [PATCH 5/5] cpufreq: Add support for actual freq

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Message-ID: <20100324140257.GA29754@aftab>
Date:	Wed, 24 Mar 2010 15:02:57 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Thomas Renninger <trenn@...e.de>
Cc:	akpm@...ux-foundation.org, davej@...hat.com,
	cpufreq@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, lenb@...nel.org
Subject: Re: [PATCH 5/5] cpufreq: Add support for actual freq

From: Thomas Renninger <trenn@...e.de>
Date: Tue, Mar 23, 2010 at 04:12:18PM +0100

Hi Thomas,

> would return the average freq of the last seconds, exactly the same
> what you can do with cpufreq-aperf from userspace.
> But if another user app does the same, it's messed up.
> You can find out the pid of the process doing the cat and remember
> aperf/mperf for it if it does not exist yet..., but now it gets to a
> point where cpufreq-aperf is really more convenient and straight foward.
> 
> Possibly documenting cpufreq-aperf in Documentation/cpu-freq would
> be worth it. Also mentioning "boost" somewhere would be great:
> grep -i boost Documentation/cpu-freq/ -r
> Documentation/cpu-freq/pcc-cpufreq.txt:This is due to "turbo boost" ...
> 
> Another idea is to have a separate cpufreq_avg_freq and update it on
> every target() call, but that's overhead...

you got me persuaded - if we want to have the effective frequency
reported in the kernel, we have to come up with a slick solution that
wouldn't incur overhead and won't be disrupted by others accessing those
MSRs. Let's leave it to cpufreq-aperf for now and revisit this when
needed.

Thanks.

-- 
Regards/Gruss,
Boris.

--
Advanced Micro Devices, Inc.
Operating Systems Research Center
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