linux-kernel - Re: [GIT PULL] Scheduler changes for v6.8

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Message-ID: <CAKfTPtAMacH4hKLyttLuQJjzc=D4m864MFaEEwZLG4K8RKTDYA@mail.gmail.com>
Date: Mon, 15 Jan 2024 14:26:21 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Qais Yousef <qyousef@...alina.io>
Cc: Wyes Karny <wkarny@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Juri Lelli <juri.lelli@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>
Subject: Re: [GIT PULL] Scheduler changes for v6.8

On Mon, 15 Jan 2024 at 13:09, Qais Yousef <qyousef@...alina.io> wrote:
>
> On 01/15/24 09:21, Vincent Guittot wrote:
>
> > > Or I've done the math wrong :-) But the two don't behave the same for the same
> > > kernel with and without CPPC.
> >
> > They will never behave the same because they can't
> > - with invariance, the utilization is the utilization at max capacity
> > so we can easily jump several OPP to go directly to the right one
> > - without invariance, the utilization is the utilization at current
> > OPP so we can only jump to a limited number of OPP
>
> I am probably missing some subtlty, but the  behavior looks more sensible to
> me when we divide by current capacity instead of max one.
>
> It seems what you're saying is that the capacity range for each OPP is 0-1024.

Yes that's the case when you don't have frequency invariance

> And that's when we know that we saturated the current capacity level we decide
> to move on.

yes

>
> As I am trying to remove the hardcoded headroom values I am wary of another
> one. But it seems this is bandaid scenario anyway; so maybe I shouldn't worry
> too much about it.
>
>
> Cheers
>
> --
> Qais Yousef