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

From: Qais Yousef <qyousef@layalina.io>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Juri Lelli <juri.lelli@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>
Subject: Re: [GIT PULL] Scheduler changes for v6.8
Date: Fri, 12 Jan 2024 18:18:05 +0000	[thread overview]
Message-ID: <20240112181805.bjvrkvvkszdfa7co@airbuntu> (raw)
In-Reply-To: <4405adb5-0b16-4716-9542-47d8bb1737ee@arm.com>

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@linux-foundation.org> wrote:
> >>
> >> On Thu, 11 Jan 2024 at 09:45, Linus Torvalds
> >> <torvalds@linux-foundation.org> wrote:
> >>>
> >>> On Thu, 11 Jan 2024 at 00:11, Vincent Guittot
> >>> <vincent.guittot@linaro.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.

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.