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From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Thu, 11 Jan 2024 14:04:04 +0100
Message-ID: <CAKfTPtCR5U++CF93aUq8i+j9G5nLRvUUbCESX=CwemYu9LKOqQ@mail.gmail.com>
Subject: Re: [GIT PULL] scheduler fixes
To: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, linux-kernel@vger.kernel.org, 
	Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, 
	Juri Lelli <juri.lelli@redhat.com>, Dietmar Eggemann <dietmar.eggemann@arm.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>
Content-Type: text/plain; charset="UTF-8"

On Thu, 11 Jan 2024 at 12:09, Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> > On Wed, 10 Jan 2024 at 14:41, Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > It's one of these two:
> > >
> > >   f12560779f9d sched/cpufreq: Rework iowait boost
> > >   9c0b4bb7f630 sched/cpufreq: Rework schedutil governor performance estimation
> > >
> > > one more boot to go, then I'll try to revert whichever causes my
> > > machine to perform horribly much worse.
> >
> > I guess it should come as no surprise that the result is
> >
> >    9c0b4bb7f6303c9c4e2e34984c46f5a86478f84d is the first bad commit
> >
> > but to revert cleanly I will have to revert all of
> >
> >       b3edde44e5d4 ("cpufreq/schedutil: Use a fixed reference frequency")
> >       f12560779f9d ("sched/cpufreq: Rework iowait boost")
> >       9c0b4bb7f630 ("sched/cpufreq: Rework schedutil governor
> > performance estimation")
> >
> > This is on a 32-core (64-thread) AMD Ryzen Threadripper 3970X, fwiw.
> >
> > I'll keep that revert in my private test-tree for now (so that I have
> > a working machine again), but I'll move it to my main branch soon
> > unless somebody has a quick fix for this problem.
>
> Thanks a lot for bisecting this, and ack on the revert in any case, these
> are relatively fresh changes that clearly didn't get enough testing - sorry!

b3edde44e5d4 ("cpufreq/schedutil: Use a fixed reference frequency") is
linked with other patches.
I can provide a clean revert of only :
f12560779f9d ("sched/cpufreq: Rework iowait boost")
9c0b4bb7f630 ("sched/cpufreq: Rework schedutil governor performance estimation")

if the fix that i proposed doesn't work:
https://lore.kernel.org/all/ZZ+ixagkxRPYyTCE@vingu-book/

>
> I also made the revert in sched/urgent & added a changelog, which you can
> pull from:
>
>    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-2024-01-11
>
>    # HEAD: 250ce3c1169743f3575cc5937fccd72380052795 Revert "sched/cpufreq: Rework schedutil governor performance estimation" and dependent commits
>
> Revert recent changes to the sched_util logic, to address a bad
> performance regression that increased kernel build time on Linus's
> 64-CPU desktop system substantially.
>
> Lightly build and boot tested.
>
>  Thanks,
>
>         Ingo
>
> ------------------>
> Ingo Molnar (1):
>       Revert "sched/cpufreq: Rework schedutil governor performance estimation" and dependent commits
>
>
>  include/linux/energy_model.h     |  1 +
>  kernel/sched/core.c              | 90 +++++++++++++++++++++++-----------------
>  kernel/sched/cpufreq_schedutil.c | 90 ++++++++++++----------------------------
>  kernel/sched/fair.c              | 22 ++--------
>  kernel/sched/sched.h             | 84 +++++++++++++++++++++++++++++++++----
>  5 files changed, 160 insertions(+), 127 deletions(-)