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

    >
    > =========================================================================================
    > 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

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