linux-kernel - Re: [PATCH v3 0/4] sched/pelt: Relax the sync of *_sum with *

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Date:   Wed, 12 Jan 2022 16:53:52 +0530
From:   Sachin Sant <sachinp@...ux.vnet.ibm.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        rickyiu@...gle.com, odin@...d.al, naresh.kamboju@...aro.org
Subject: Re: [PATCH v3 0/4]   sched/pelt: Relax the sync of *_sum with *_avg


> On 11-Jan-2022, at 7:16 PM, Vincent Guittot <vincent.guittot@...aro.org> wrote:
> 
> Rick reported performance regressions in bugzilla because of cpu
> frequency being lower than before:
>    https://bugzilla.kernel.org/show_bug.cgi?id=215045
> 
> He bisected the problem to:
> commit 1c35b07e6d39 ("sched/fair: Ensure _sum and _avg values stay consistent")
> 
> More details are available in commit message of patch 1.
> 
> This patchset reverts the commit above and adds several checks when
> propagating the changes in the hierarchy to make sure that we still have
> coherent util_avg and util_sum.
> 
> Dietmar found a simple way to reproduce the WARN fixed by 
> commit 1c35b07e6d39 ("sched/fair: Ensure _sum and _avg values stay consistent")
> by looping on hackbench in several different sched group levels.
> 
> This patchset as run on the reproducer with success but it probably needs
> more tests by people who faced the WARN before.
> 

I ran scheduler regression tests(including cfg_bandwidth) from LTP
for about 6 hours. I did not observe any (new or previously reported)
kernel warn messages.

Based on this test result for ppc64le
Tested-by: Sachin Sant <sachinp@...ux.ibm.com>

-Sachin