linux-kernel - Re: [RFC PATCH 1/1] sched/pelt: Introduce PELT multiplier

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Message-ID: <CAKfTPtCN6fmTZ8mvDWP80_KF2CVdv8AkyB=VKvSvD_HH19ZwVg@mail.gmail.com>
Date:   Tue, 6 Sep 2022 07:49:28 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Vincent Donnefort <vdonnefort@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Abhijeet Dharmapurikar <adharmap@...cinc.com>,
        Jian-Min <Jian-Min.Liu@...iatek.com>,
        Qais Yousef <qais.yousef@....com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] sched/pelt: Introduce PELT multiplier

On Fri, 2 Sept 2022 at 09:54, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 29/08/2022 12:13, Vincent Guittot wrote:
> > On Mon, 29 Aug 2022 at 12:03, Peter Zijlstra <peterz@...radead.org> wrote:
> >>
> >> On Mon, Aug 29, 2022 at 10:08:13AM +0200, Peter Zijlstra wrote:
> >>> On Mon, Aug 29, 2022 at 07:54:50AM +0200, Dietmar Eggemann wrote:
> >>>> From: Vincent Donnefort <vincent.donnefort@....com>
>
> [...]
>
> >>> Hurmph... I'd almost go write you something like
> >>> static_call()/static_branch() but for immediates.
> >>>
> >>> That said; given there's only like 3 options, perhaps a few
> >>> static_branch() instances work just fine ?
> >>
> >> Also, I'm not at all sure about exposing that as an official sysctl.
> >
> > Me too, I would even make it a boot time parameter so we can remove
>
> Isn't a sched feature even less official than a boot parameter?
> But AFAIK at least some of the Android folks want to change this during
> runtime and they don't have debugfs mounted.
>
> > the new clock_task_mult clock and left shift clock_taslk or the delta
> > before passing it to clock_pelt
>
> We still need rq_clock_task_mult(rq), i.e. `rq->clock_task_mult` in
> _update_idle_rq_clock_pelt() though.

Why ? If the mult is defined at boot we just have to use
"rq_clock_task(rq) << mult" instead of rq_clock_task(rq) when updating
clock_pelt