linux-kernel - Re: [LKP] [sched/fair] 070f5e860e: reaim.jobs_per

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Date:   Wed, 24 Jun 2020 11:04:35 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Cc:     Hillf Danton <hdanton@...a.com>,
        kernel test robot <rong.a.chen@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Phil Auld <pauld@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LKP] [sched/fair] 070f5e860e: reaim.jobs_per_min -10.5% regression

On Fri, 19 Jun 2020 at 09:15, Vincent Guittot
<vincent.guittot@...aro.org> wrote:
>
> On Fri, 19 Jun 2020 at 06:55, Xing Zhengjun
> <zhengjun.xing@...ux.intel.com> wrote:
> > On 6/17/2020 10:57 PM, Vincent Guittot wrote:
> > > Le mercredi 17 juin 2020 à 08:30:21 (+0800), Xing Zhengjun a écrit :
>
> ...
>
> > > OK. So the regression disappears when the conditions on runnable_avg are removed.
> > >
> > > In the meantime, I have been able to understand more deeply what was happeningi
> > > for this bench and how it is impacted by
> > >    commit: 070f5e860ee2 ("sched/fair: Take into account runnable_avg to classify group")
> > >
> > > This bench forks a new thread for each and every new step. But a newly forked
> > > threads start with a load_avg and a runnable_avg set to max whereas the threads
> > > are running shortly before exiting. This makes the CPU to be set overloaded in
> > > some case whereas it isn't.
> > >
> > > Could you try the patch below ?
> > > It fixes the problem on my setup (I have finally been able to reproduce the problem)
> > >
> > > ---
> > >   kernel/sched/fair.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index 0aeffff62807..b33a4a9e1491 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -807,7 +807,7 @@ void post_init_entity_util_avg(struct task_struct *p)
> > >               }
> > >       }
> > >
> > > -     sa->runnable_avg = cpu_scale;
> > > +     sa->runnable_avg = sa->util_avg;
> > >
> > >       if (p->sched_class != &fair_sched_class) {
> > >               /*
> > >
> >
> > I apply the patch above based on v5.7, the test result is as the following:
>
> Thanks for the tests.
>
> This patch fixes the regression on the test. I'm going to run more
> tests to make sure that it doesn't regress others benchmarks. I
> remember that some were slightly better with the original behavior but
> others patches and fixes have been added in the meantime that might
> change the results.

I have run more test on large and small system and the results are
balanced. I might see a small regression on some hackbenchs results on
large system but it's in the range of the stdev and might not be
significant

I'm going to send  a clean patch with a commit message.

Thanks for your help
Vincent

>
> >
> > =========================================================================================
> > tbox_group/testcase/rootfs/kconfig/compiler/runtime/nr_task/debug-setup/test/cpufreq_governor/ucode:
> >
> > lkp-ivb-d04/reaim/debian-x86_64-20191114.cgz/x86_64-rhel-7.6/gcc-7/300s/100%/test/five_sec/performance/0x21
> >
> > commit:
> >    9f68395333ad7f5bfe2f83473fed363d4229f11c
> >    070f5e860ee2bf588c99ef7b4c202451faa48236
> >    v5.7
> >    cbb4d668e7431479a7978fa79d64c2271adefab0 ( the test patch which modify
> > post_init_entity_util_avg())
> >
> > 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2                        v5.7
> > cbb4d668e7431479a7978fa79d6
> > ---------------- --------------------------- ---------------------------
> > ---------------------------
> >           %stddev     %change         %stddev     %change
> > %stddev     %change         %stddev
> >               \          |                \          |                \
> >          |                \
> >        0.69           -10.3%       0.62            -9.1%       0.62
> >        +0.6%       0.69        reaim.child_systime
> >        0.62            -1.0%       0.61            +0.5%       0.62
> >        -0.3%       0.62        reaim.child_utime
> >       66870           -10.0%      60187            -7.6%      61787
> >        +0.7%      67335        reaim.jobs_per_min
>
>
>
> >       16717           -10.0%      15046            -7.6%      15446
> >        +0.7%      16833        reaim.jobs_per_min_child
> >       97.84            -1.1%      96.75            -0.4%      97.43
> >        +0.2%      98.05        reaim.jti
> >       72000           -10.8%      64216            -8.3%      66000
> >        +0.0%      72000        reaim.max_jobs_per_min
> >        0.36           +10.6%       0.40            +7.8%       0.39
> >        -0.6%       0.36        reaim.parent_time
> >        1.58 ±  2%     +71.0%       2.70 ±  2%     +26.9%       2.01 ±
> > 2%      -8.8%       1.44 ±  2%  reaim.std_dev_percent
> >        0.00 ±  5%    +110.4%       0.01 ±  3%     +48.8%       0.01 ±
> > 7%     -24.6%       0.00 ±  7%  reaim.std_dev_time
> >       50800            -2.4%      49600            -1.6%      50000
> >        +0.0%      50800        reaim.workload
> >
> >
> > --
> > Zhengjun Xing