linux-kernel - Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins

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Message-ID: <20230912142821.GA22166@noisy.programming.kicks-ass.net>
Date:   Tue, 12 Sep 2023 16:28:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Qais Yousef <qyousef@...alina.io>,
        Chris Redpath <Chris.Redpath@....com>
Subject: Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins

On Tue, Sep 12, 2023 at 12:51:52PM +0100, Lukasz Luba wrote:

> You can see the util signal of that 'CrRendererMain' task and those
> utilization drops in time, which I was referring to. When the util
> drops below some threshold, the task might 'fit' into smaller CPU,
> which could be prevented automatically byt maintaining the util est
> for longer (but not for all).

Right, so right at those util_est dips it has some small activations.
It's like a poll loop or something instead of a full block waiting for
things to happen.

And yeah, that'll destroy util_est in a hurry :/

> I do like your idea that Util EST might be per-task. I'm going to
> check this, because that might help to get rid of the overutilized state
> which is probably because small tasks are also 'bigger' for longer.
> 
> If this util est have chance to fly upstream, I could send an RFC if
> you don't mind.

The biggest stumbling block I see is the user interface; some generic
QoS hints based thing that allows us to do random things -- like tune
the above might do, dunno.