Re: [LKP] [sched/fair] 070f5e860e: reaim.jobs_per_min -10.5% regression

[Vincent Guittot]

On Fri, 19 Jun 2020 at 06:55, Xing Zhengjun
<zhengjun.xing@xxxxxxxxxxxxxxx> wrote:
> On 6/17/2020 10:57 PM, Vincent Guittot wrote:
> > Le mercredi 17 juin 2020 Ã 08:30:21 (+0800), Xing Zhengjun a Ãcrit :

...

> > 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.

>
> =========================================================================================
> 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 Â  2%     +71.0%       2.70 Â  2%     +26.9%       2.01 Â
> 2%      -8.8%       1.44 Â  2%  reaim.std_dev_percent
>        0.00 Â  5%    +110.4%       0.01 Â  3%     +48.8%       0.01 Â
> 7%     -24.6%       0.00 Â  7%  reaim.std_dev_time
>       50800            -2.4%      49600            -1.6%      50000
>        +0.0%      50800        reaim.workload
>
>
> --
> Zhengjun Xing