linux-kernel - Re: [sched/fair] b360fb5e59: stress-ng.vm-segv.ops_per

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Date:   Wed, 03 Mar 2021 18:34:13 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     0day robot <lkp@...el.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>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        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]  b360fb5e59:  stress-ng.vm-segv.ops_per_sec -13.9% regression

On 23/02/21 12:36, Valentin Schneider wrote:
> On 23/02/21 10:30, kernel test robot wrote:
>> Greeting,
>>
>> FYI, we noticed a -13.9% regression of stress-ng.vm-segv.ops_per_sec due to commit:
>>
>>
>> commit: b360fb5e5954a8a440ef95bf11257e2e7ea90340 ("[PATCH v2 1/7] sched/fair: Ignore percpu threads for imbalance pulls")
>> url: https://github.com/0day-ci/linux/commits/Valentin-Schneider/sched-fair-misfit-task-load-balance-tweaks/20210219-211028
>> base: https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git c5e6fc08feb2b88dc5dac2f3c817e1c2a4cafda4
>>
>> in testcase: stress-ng
>> on test machine: 96 threads Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 512G memory
>> with following parameters:
>>
>>      nr_threads: 10%
>>      disk: 1HDD
>>      testtime: 60s
>>      fs: ext4
>>      class: vm
>>      test: vm-segv
>>      cpufreq_governor: performance
>>      ucode: 0x5003003
>>

So I've been running this on my 32 CPU arm64 desktop with:
  nr_threads: 10%
  nr_threads: 50%
  (20 iterations each)

In the 50% case I see a ~2% improvement, in the 10% a -0.3%
regression (another batch showed -0.08%)... Still far off from the reported
-14%. If it's really required I can go find an x86 box to test this on, but
so far it looks like a fluke.