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

Vincent Guittot
2020-06-24T09:04:51Z

On Fri, 19 Jun 2020 at 09:15, Vincent Guittot
<vincent.guittot@linaro.org> wrote:
>
> On Fri, 19 Jun 2020 at 06:55, Xing Zhengjun
> <zhengjun.xing@linux.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