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

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Date:   Thu, 22 Oct 2020 14:07:38 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        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 Mailing List <linux-kernel@...r.kernel.org>,
        Quentin Perret <qperret@...gle.com>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Lukasz Luba <lukasz.luba@....com>
Subject: Re: [PATCH 2/2] thermal: cpufreq_cooling: Reuse effective_cpu_util()

On Thu, Oct 22, 2020 at 1:58 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Oct 22, 2020 at 01:30:01PM +0200, Rafael J. Wysocki wrote:
>
> > Many people use intel_pstate in the active mode with HWP enabled too.
>
> We now have HWP-passive supported, afaict. So we should discourage that.

Which is kind of hard, because plain HWP does better in some cases,
especially performance-focused.

I am still not sure why this is the case given how the passive mode
with HWP enabled is implemented, but that's what Srinivas sees in his
tests.

> That is; I'll care less and less about people not using schedutil as
> time goes on.
>
> > Arguably, that doesn't need to compute the effective utilization, so I
> > guess it is not relevant for the discussion here, but it is not
> > negligible in general.
>
> Why not? cpufreq-cooling should still be able to throttle the system by
> setting HWP.Highest_Performance no?

Well, in theory, but it is not used on x86 AFAICS.

> In which case it still needs an energy estimate.