linux-kernel - Re: [RFC PATCH 0/6] sched: uclamp sum aggregation

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Message-ID: <CAKfTPtD10c4Uif6EATJ2SiAPdnEzXkC78nZE=q23dLM7fszvEQ@mail.gmail.com>
Date:   Tue, 5 Dec 2023 17:26:46 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Hongyan Xia <hongyan.xia2@....com>
Cc:     Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Lukasz Luba <lukasz.luba@....com>,
        Christian Loehle <christian.loehle@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/6] sched: uclamp sum aggregation

On Tue, 5 Dec 2023 at 16:19, Hongyan Xia <hongyan.xia2@....com> wrote:
>
> On 04/12/2023 16:12, Vincent Guittot wrote:
> > On Mon, 4 Dec 2023 at 02:48, Hongyan Xia <hongyan.xia2@....com> wrote:
> >>
> >> [...]
> >>
> >> Other shortcomings are not that critical, but the fact that uclamp_min's
> >> effectiveness is divided by N under max aggregation I think is not
> >> acceptable.
> >
> > Change EAS task placement policy in this case to take into account
> > actual utilization and uclamp_min/max
>
> Thank you. I agree. I want to emphasize this specifically because this
> is exactly what I'm trying to do. The whole series can be rephrased in a
> different way:
>
> - The PELT signal is distorted when uclamp is active.

Sorry but no it's not

> - Let's consider the [PELT, uclamp_min, uclamp_max] tuple.

That's what we are already doing with effective_cpu_util. We might
want to improve how we use them in EAS but that's another story than
your proposal

> - Always carrying all three variables is too much, but [PELT,
> clamped(PELT)] is an approximation that works really well.

As said before. It's a no go for this mix

>
> Of course, I'll explore if there's a way to make things less messy. I
> just realized why I didn't do things util_est way but instead directly
> clamping on PELT, it's because util_est boosts util_avg and can't work
> for uclamp_max. I'll keep exploring options.
>
> >> [...]