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

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Date:   Thu, 22 Apr 2021 10:55:10 +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 15:47, Oliver Sang wrote:
> hi, Valentin Schneider,
>
> On Wed, Apr 21, 2021 at 11:27:49AM +0100, Valentin Schneider wrote:
>> On 21/04/21 11:20, Oliver Sang wrote:
>> > what's the machine model you used upon which the regression cannot be reproduced?
>> > we could check if we have similar model then re-check on the our machine.
>> >
>> 
>> I tested this on:
>> o Ampere eMAG (arm64, 32 cores)
>> o 2-socket Xeon E5-2690 (x86, 40 cores)
>> 
>> and found at worse a -0.3% regression and at best a 2% improvement. I know
>> that x86 box is somewhat ancient, but it's been my go-to "have I broken
>> x86?" test victim for a while :-)
>
> we don't have exactly 2-socket Xeon E5-2690 model, but we have one:
> Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz (2-socket, 48 cores with 112G memory)
> the test on it shows the regression is existing, too. but smaller (-5.3%)
> hope it's helpful
>

It is, thank you for trying this out on another system and figuring out
it's still visible! I'll go find myself some other x86 box and dig into it;
I'd rather not leave this hanging for too long.