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

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Date:   Fri, 2 Sep 2022 09:53:50 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     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 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.