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SubjectRe: [PATCH RFC 0/3] Per-process power consumption measurement facility
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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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