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

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Message-ID: <87mttqt5jc.mognet@arm.com>
Date:   Thu, 22 Apr 2021 21:42:31 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Oliver Sang <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 22/04/21 10:55, Valentin Schneider wrote:
> I'll go find myself some other x86 box and dig into it;
> I'd rather not leave this hanging for too long.

So I found myself a dual-socket Xeon Gold 5120 @ 2.20GHz (64 CPUs) and
*there* I get a somewhat consistent ~-6% regression. As I'm suspecting
cacheline shenanigans, I also ran that with Peter's recent
kthread_is_per_cpu() change, and that brings it down to ~-3%

I'll leave it at here for today, but at least that's something I can work
with.