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

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Date:   Mon, 19 Oct 2020 13:10:37 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        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 30-07-20, 12:16, Lukasz Luba wrote:
> Hi Viresh,
> 
> On 7/30/20 7:24 AM, Viresh Kumar wrote:
> > 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.
> > 
> 
> I don't think that these two are separate. Furthermore, I think we
> would need this kind of information also in future in the powercap.
> I've discussed with Daniel this possible scenario.
> 
> We have a vendor who presented issue with the IPA input power and
> pointed out these issues. Unfortunately, I don't have this vendor
> phone but I assume it can last a few minutes without changing the
> max allowed OPP. Based on their plots the frequency driven by the
> governor is changing, also the idles are present during the IPA period.
> 
> Please give me a few days, because I am also plumbing these stuff
> and would like to present it. These two interfaces: involving cpufreq
> driver or fallback mode for utilization and EM.

Its been almost 3 months, do we have any update for this? We really
would like to get this patchset merged in some form as it provides a
simple update and I think more work can be done by anyone over it in
future.

-- 
viresh