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

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Date: Fri, 12 Jan 2024 17:58:18 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: 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 15:23, Dietmar Eggemann <dietmar.eggemann@....com> 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'.

Thanks for the tests

>
> f12560779f9d - sched/cpufreq: Rework iowait boost                              <- (w/ patches)
> 9c0b4bb7f630 - sched/cpufreq: Rework schedutil governor performance estimation
> 50181c0cff31 - sched/pelt: Avoid underestimation of task utilization           <- (base)
> ...
>
> # cpufreq-info -c 0 -e
> ...
> analyzing CPU 0:
>   driver: acpi-cpufreq
>   CPUs which run at the same hardware frequency: 0
>   CPUs which need to have their frequency coordinated by software: 0
>   maximum transition latency: 10.0 us.
>   hardware limits: 1.20 GHz - 3.00 GHz
>   available frequency steps: 3.00 GHz, 3.00 GHz, 2.90 GHz, 2.70 GHz, 2.60 GHz, 2.50 GHz, 2.40 GHz, 2.20 GHz,
>                              2.10 GHz, 2.00 GHz, 1.80 GHz, 1.70 GHz, 1.60 GHz, 1.50 GHz, 1.30 GHz, 1.20 GHz
>   available cpufreq governors: conservative, ondemand, userspace, powersave, performance, schedutil
>   current policy: frequency should be within 1.20 GHz and 3.00 GHz.
>                   The governor "schedutil" may decide which speed to use
>                   within this range.
>   current CPU frequency is 1.20 GHz (asserted by call to hardware).
>
>
> cpufreq is still fast-switching, so no schedutil 'sugov' DL threads.