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

From: Vincent Guittot <vincent.guittot@linaro.org>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Vincent Donnefort <vdonnefort@google.com>,
	Quentin Perret <qperret@google.com>,
	Patrick Bellasi <patrick.bellasi@matbug.net>,
	Abhijeet Dharmapurikar <adharmap@quicinc.com>,
	Jian-Min <Jian-Min.Liu@mediatek.com>,
	Qais Yousef <qais.yousef@arm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/1] sched/pelt: Introduce PELT multiplier
Date: Tue, 6 Sep 2022 07:49:28 +0200	[thread overview]
Message-ID: <CAKfTPtCN6fmTZ8mvDWP80_KF2CVdv8AkyB=VKvSvD_HH19ZwVg@mail.gmail.com> (raw)
In-Reply-To: <12b3443a-6456-4a57-95b3-dd6be5b10873@arm.com>

On Fri, 2 Sept 2022 at 09:54, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>
> On 29/08/2022 12:13, Vincent Guittot wrote:
> > On Mon, 29 Aug 2022 at 12:03, Peter Zijlstra <peterz@infradead.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@arm.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