linux-kernel - Re: [PATCH RFC 0/3] Per-process power consumption measurement facility

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Message-ID: <17414140.5WcljOZAKe@vostro.rjw.lan>
Date:	Tue, 30 Jul 2013 15:31:50 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Konstantin Krivyakin <k.krivyakin@...sung.com>,
	linux-kernel@...r.kernel.org, viresh.kumar@...aro.org,
	mingo@...hat.com, kgene.kim@...sung.com, linux-pm@...r.kernel.org,
	i.zhbanov@...sung.com, e.voevodin@...sung.com,
	kyungmin.park@...sung.com, akpm@...ux-foundation.org
Subject: Re: [PATCH RFC 0/3] Per-process power consumption measurement facility

On Tuesday, July 30, 2013 10:52:56 AM Peter Zijlstra wrote:
> On Tue, Jul 30, 2013 at 12:17:36PM +0400, Konstantin Krivyakin wrote:
> > This patchset adds per-process power consumption measurement facility.
> > Power consumption is very important on mobile platforms. This code
> > allows to measure consumed power in Watts*Hours. The consumed power
> > for process is updated on scheduler switch and depends on current
> > CPU voltage and frequency.
> > 
> > The formula for computation is: P = C * V^2 * f, where C is a constant
> > that reflects capacity of the system, V is the current voltage and
> > f is the current frequency.
> > (Taken from: http://en.wikipedia.org/wiki/CPU_power_dissipation).
> > 
> > In this patchset was added implementation for Exynos platform
> > to demonstrate how it works.
> > 
> > To minimize scheduler impact for each CPU P-state the value of (V^2 *f)
> > was precomputed at the time of platform initialization.
> 
> It seems to me the 3 multiplies that takes could be done when cpufreq
> actually changes the P-state.
> 
> > And to reduce performance impact furthermore, the C constant is multiplied
> > in userspace.
> 
> That seems particularly silly; how is userspace to know C and why
> isn't it a much better idea to do this in the code generating the number
> for userspace to consume.
> 
> Also, I intensely dislike this thing because:
> 
>  - it adds more user interface
>  - it adds more accounting muck
>  - it completely lacks any useful changelogs
>  - it completely fails to even begin addressing the issues we already
>    have with cpufreq
> 
> There's been a lot of talk about power aware scheduling in the recent
> past, there's also been a lot of problems listed we must overcome/solve.
> This patch set completely fails to tie into any of that.
> 
> You also completely fail to explain the user case and thus related why
> you can't use any of the other facilities like perf or ftrace to measure
> this.

Agreed, thanks Peter!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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