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List:       linux-kernel
Subject:    Re: [GIT PULL] scheduler fixes
From:       Vincent Guittot <vincent.guittot () linaro ! org>
Date:       2024-01-11 13:04:04
Message-ID: CAKfTPtCR5U++CF93aUq8i+j9G5nLRvUUbCESX=CwemYu9LKOqQ () mail ! gmail ! com
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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(-)


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