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

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Date: Fri, 12 Jan 2024 20:03:36 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Qais Yousef <qyousef@...alina.io>
Cc: Dietmar Eggemann <dietmar.eggemann@....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>, 
	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 Fri, 12 Jan 2024 at 19:18, Qais Yousef <qyousef@...alina.io> wrote:
>
> On 01/12/24 15:23, Dietmar Eggemann wrote:
> > On 11/01/2024 19:16, Vincent Guittot wrote:
> > > On Thu, 11 Jan 2024 at 18:53, Linus Torvalds
> > > <torvalds@...ux-foundation.org> wrote:
> > >>
> > >> On Thu, 11 Jan 2024 at 09:45, Linus Torvalds
> > >> <torvalds@...ux-foundation.org> wrote:
> > >>>
> > >>> On Thu, 11 Jan 2024 at 00:11, Vincent Guittot
> > >>> <vincent.guittot@...aro.org> wrote:
> > >>>>
> > >>>> Could you confirm that cpufreq governor is schedutil and the driver is
> > >>>> amd-pstate on your system ?
> > >>>
> > >>> schedutil yes, amd-pstate no. I actually just use acpi_cpufreq
> > >>
> > >> Bah. Hit 'send' mistakenly too soon, thus the abrupt end and
> > >> unfinished quoting removal.
> > >>
> > >> And don't ask me why it's acpi_pstate-driven. I have X86_AMD_PSTATE=y, but
> > >>
> > >>     /sys/devices/system/cpu/cpufreq/policy0/scaling_driver
> > >>
> > >> clearly says 'acpi-cpufreq'. Maybe I'm looking in the wrong place. My dmesg says
> > >
> > > That seems to be the right place to look
> > >
> > >>
> > >>     amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled
> > >>
> > >> which is presumably the reason my machine uses acpi-pstate.
> > >>
> > >> I will also test out your other questions, but I need to go back and
> > >> do more pull requests first.
> > >
> > > ok, thanks
> > >
> > > I'm going to continue checking what else could trigger such regression
> > > having in mind that your system should not have beeb impacted by this
> > > changes
> >
> > I can't see the regression on my
> >
> >   20-core (40-thread) Intel Xeon CPU E5-2690 v2
> >
> > with 'schedutil' and 'acpi-cpufreq'.
>
> I tried to reproduce on AMD 3900X 12-Core system. I don't see any difference
> in compiling defconfig with and without the two patches reverted. ~1m26s.

Thanks for testing.
I haven't been able to reproduce the problem too. But my system are
quite different

>
> using schedutil and acpi-cpufreq driver too.
>
> I disabled CONFIG_UCLAMP_TASK and that didn't make a difference.
>
> I would have expected the iowait boost to be the more troublesome being the
> more subtle one tbh.