linux-kernel - Re: [PATCH 2/2] thermal: cpufreq_cooling: Reuse effective_cpu

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Date:   Thu, 30 Jul 2020 11:54:14 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Lukasz Luba <lukasz.luba@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Quentin Perret <qperret@...gle.com>,
        Rafael Wysocki <rjw@...ysocki.net>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 2/2] thermal: cpufreq_cooling: Reuse effective_cpu_util()

On 17-07-20, 11:46, Vincent Guittot wrote:
> On Thu, 16 Jul 2020 at 16:24, Lukasz Luba <lukasz.luba@....com> wrote:
> > On 7/16/20 12:56 PM, Peter Zijlstra wrote:
> > > Currently cpufreq_cooling appears to estimate the CPU energy usage by
> > > calculating the percentage of idle time using the per-cpu cpustat stuff,
> > > which is pretty horrific.
> >
> > Even worse, it then *samples* the *current* CPU frequency at that
> > particular point in time and assumes that when the CPU wasn't idle
> > during that period - it had *this* frequency...
> 
> So there is 2 problems in the power calculation of cpufreq cooling device :
> - How to get an accurate utilization level of the cpu which is what
> this patch is trying to fix because using idle time is just wrong
> whereas scheduler utilization is frequency invariant

Since this patch is targeted only towards fixing this particular
problem, should I change something in the patch to make it acceptable
?

> - How to get power estimate from this utilization level. And as you
> pointed out, using the current freq which is not accurate.

This should be tackled separately I believe.

-- 
viresh