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Date:   Fri, 15 May 2020 09:43:39 +0800
From:   Oliver Sang <oliver.sang@...el.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...nel.org>, Ben Segall <bsegall@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Mike Galbraith <efault@....de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        OTC LSE PnP <otc.lse.pnp@...el.com>, oliver.sang@...el.com
Subject: Re: [sched/fair] 0b0695f2b3:
 phoronix-test-suite.compress-gzip.0.seconds 19.8% regression

On Thu, May 14, 2020 at 07:09:35PM +0200, Vincent Guittot wrote:
> Hi Oliver,
> 
> On Thu, 14 May 2020 at 16:05, kernel test robot <oliver.sang@...el.com> wrote:
> >
> > Hi Vincent Guittot,
> >
> > Below report FYI.
> > Last year, we actually reported an improvement "[sched/fair] 0b0695f2b3:
> > vm-scalability.median 3.1% improvement" on link [1].
> > but now we found the regression on pts.compress-gzip.
> > This seems align with what showed in "[v4,00/10] sched/fair: rework the CFS
> > load balance" (link [2]), where showed the reworked load balance could have
> > both positive and negative effect for different test suites.
> 
> We have tried to run  all possible use cases but it's impossible to
> covers all so there were a possibility that one that is not covered,
> would regressed.
> 
> > And also from link [3], the patch set risks regressions.
> >
> > We also confirmed this regression on another platform
> > (Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz with 8G memory),
> > below is the data (lower is better).
> > v5.4    4.1
> > fcf0553db6f4c79387864f6e4ab4a891601f395e    4.01
> > 0b0695f2b34a4afa3f6e9aa1ff0e5336d8dad912    4.89
> > v5.5    5.18
> > v5.6    4.62
> > v5.7-rc2    4.53
> > v5.7-rc3    4.59
> >
> > It seems there are some recovery on latest kernels, but not fully back.
> > We were just wondering whether you could share some lights the further works
> > on the load balance after patch set [2] which could cause the performance
> > change?
> > And whether you have plan to refine the load balance algorithm further?
> 
> I'm going to have a look at your regression to understand what is
> going wrong and how it can be fixed

Thanks a lot!

> 
> Thanks
> Vincent
> 

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