linux-kernel - Re: [sched/fair] 38ac256d1c: stress-ng.vm-segv.ops_per

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Date:   Wed, 14 Apr 2021 18:17:38 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     0day robot <lkp@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        ying.huang@...el.com, feng.tang@...el.com, zhengjun.xing@...el.com,
        Lingutla Chandrasekhar <clingutla@...eaurora.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Quentin Perret <qperret@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Rik van Riel <riel@...riel.com>, aubrey.li@...ux.intel.com,
        yu.c.chen@...el.com
Subject: Re: [sched/fair]  38ac256d1c:  stress-ng.vm-segv.ops_per_sec -13.8% regression

On 14/04/21 13:21, kernel test robot wrote:
> Greeting,
>
> FYI, we noticed a -13.8% regression of stress-ng.vm-segv.ops_per_sec due to commit:
>
>
> commit: 38ac256d1c3e6b5155071ed7ba87db50a40a4b58 ("[PATCH v5 1/3] sched/fair: Ignore percpu threads for imbalance pulls")
> url: https://github.com/0day-ci/linux/commits/Valentin-Schneider/sched-fair-load-balance-vs-capacity-margins/20210408-060830
> base: https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git 0a2b65c03e9b47493e1442bf9c84badc60d9bffb
>
> in testcase: stress-ng
> on test machine: 96 threads Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 192G memory
> with following parameters:
>
>       nr_threads: 10%
>       disk: 1HDD
>       testtime: 60s
>       fs: ext4
>       class: os
>       test: vm-segv
>       cpufreq_governor: performance
>       ucode: 0x5003006
>
>

That's almost exactly the same result as [1], which is somewhat annoying
for me because I wasn't able to reproduce those results back then. Save
from scrounging the exact same machine to try this out, I'm not sure what's
the best way forward. I guess I can re-run the workload on whatever
machines I have and try to spot any potentially problematic pattern in the
trace...

[1]: http://lore.kernel.org/r/20210223023004.GB25487@xsang-OptiPlex-9020