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

Vincent Guittot
2020-06-17T14:57:31Z

Le mercredi 17 juin 2020 à 08:30:21 (+0800), Xing Zhengjun a écrit :
>
>
> On 6/16/2020 2:54 PM, Vincent Guittot wrote:
> >
> > Hi Xing,
> >
> > Le mardi 16 juin 2020 à 11:17:16 (+0800), Xing Zhengjun a écrit :
> > >
> > >
> > > On 6/15/2020 4:10 PM, Vincent Guittot wrote:
> > > > Hi Xing,
> > > >
> > > > Le lundi 15 juin 2020 à 15:26:59 (+0800), Xing Zhengjun a écrit :
> > > > >
> > > > >
> > > > > On 6/12/2020 7:06 PM, Hillf Danton wrote:
> > > > > >
> > > > > > On Fri, 12 Jun 2020 14:36:49 +0800 Xing Zhengjun wrote:
> > > >
> >
> > ...
> >
> > > >
> > >
> > > I apply the patch based on v5.7, the test result is as the following:
> >
> > TBH, I didn't expect that the results would still be bad, so i wonder if the threshold are
> > the root problem.
> >
> > Could you run tests with the patch below that removes condition with runnable_avg ?
> > I just want to make sure that those 2 conditions are the root cause.
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index da3e5b54715b..f5774d0af059 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -8210,10 +8210,6 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
> > if (sgs->sum_nr_running < sgs->group_weight)
> > return true;
> >
> > - if ((sgs->group_capacity * imbalance_pct) <
> > - (sgs->group_runnable * 100))
> > - return false;
> > -
> > if ((sgs->group_capacity * 100) >
> > (sgs->group_util * imbalance_pct))
> > return true;
> > @@ -8239,10 +8235,6 @@ group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
> > (sgs->group_util * imbalance_pct))
> > return true;
> >
> > - if ((sgs->group_capacity * imbalance_pct) <
> > - (sgs->group_runnable * 100))
> > - return true;
> > -
> > return false;
> > }
> >
> >
> >
> > Thanks.
> > Vincent
> >
>
>
> I apply the patch based on v5.7, the test result is as the following:
>
> =========================================================================================
> 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
> 63a5d0fbb5ec62f5148c251c01e709b8358cd0ee (the test patch)
>
> 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2 v5.7
> 63a5d0fbb5ec62f5148c251c01e
> ---------------- --------------------------- ---------------------------
> ---------------------------
> %stddev %change %stddev %change %stddev %change
> %stddev
> \ | \ | \
> | \
> 0.69 -10.3% 0.62 -9.1% 0.62
> +1.0% 0.69 reaim.child_systime
> 0.62 -1.0% 0.61 +0.5% 0.62
> -0.1% 0.62 reaim.child_utime
> 66870 -10.0% 60187 -7.6% 61787
> +1.1% 67636 reaim.jobs_per_min
> 16717 -10.0% 15046 -7.6% 15446
> +1.1% 16909 reaim.jobs_per_min_child

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) {
/*
--
2.17.1

> 97.84 -1.1% 96.75 -0.4% 97.43
> +0.3% 98.09 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
> -1.1% 0.36 reaim.parent_time
> 1.58 ± 2% +71.0% 2.70 ± 2% +26.9% 2.01 ± 2%
> -11.9% 1.39 ± 4% reaim.std_dev_percent
> 0.00 ± 5% +110.4% 0.01 ± 3% +48.8% 0.01 ± 7%
> -27.3% 0.00 ± 15% reaim.std_dev_time
> 50800 -2.4% 49600 -1.6% 50000
> +0.0% 50800 reaim.workload
>
>
> > >
> > > =========================================================================================
> > > 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
> > > 3e1643da53f3fc7414cfa3ad2a16ab2a164b7f4d (the test patch)
> > >
> > > 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2 v5.7
> > > 3e1643da53f3fc7414cfa3ad2a1
> > > ---------------- --------------------------- ---------------------------
> > > ---------------------------
> > > %stddev %change %stddev %change %stddev %change
> > > %stddev
> > > \ | \ | \
> > > | \
> > > 0.69 -10.3% 0.62 -9.1% 0.62
> > > -7.1% 0.64 reaim.child_systime
> > > 0.62 -1.0% 0.61 +0.5% 0.62
> > > +1.3% 0.63 reaim.child_utime
> > > 66870 -10.0% 60187 -7.6% 61787
> > > -6.1% 62807 reaim.jobs_per_min
> > > 16717 -10.0% 15046 -7.6% 15446
> > > -6.1% 15701 reaim.jobs_per_min_child
> > > 97.84 -1.1% 96.75 -0.4% 97.43
> > > -0.5% 97.34 reaim.jti
> > > 72000 -10.8% 64216 -8.3% 66000
> > > -5.7% 67885 reaim.max_jobs_per_min
> > > 0.36 +10.6% 0.40 +7.8% 0.39
> > > +6.9% 0.38 reaim.parent_time
> > > 1.58 ± 2% +71.0% 2.70 ± 2% +26.9% 2.01 ± 2%
> > > +32.5% 2.09 ± 6% reaim.std_dev_percent
> > > 0.00 ± 5% +110.4% 0.01 ± 3% +48.8% 0.01 ± 7%
> > > +61.7% 0.01 ± 8% reaim.std_dev_time
> > > 50800 -2.4% 49600 -1.6% 50000
> > > -1.3% 50133 reaim.workload
> > >
> > >
> > > > >
> > > > > =========================================================================================
> > > > > 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
> > > > > 6b33257768b8dd3982054885ea310871be2cfe0b (Hillf's patch)
> > > > >
> > > > > 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2 v5.7
> > > > > 6b33257768b8dd3982054885ea3
> > > > > ---------------- --------------------------- ---------------------------
> > > > > ---------------------------
> > > > > %stddev %change %stddev %change %stddev %change
> > > > > %stddev
> > > > > \ | \ | \
> > > > > | \
> > > > > 0.69 -10.3% 0.62 -9.1% 0.62
> > > > > -10.1% 0.62 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
> > > > > -8.3% 61305 reaim.jobs_per_min
> > > > > 16717 -10.0% 15046 -7.6% 15446
> > > > > -8.3% 15326 reaim.jobs_per_min_child
> > > > > 97.84 -1.1% 96.75 -0.4% 97.43
> > > > > -0.5% 97.37 reaim.jti
> > > > > 72000 -10.8% 64216 -8.3% 66000
> > > > > -8.3% 66000 reaim.max_jobs_per_min
> > > > > 0.36 +10.6% 0.40 +7.8% 0.39
> > > > > +9.4% 0.39 reaim.parent_time
> > > > > 1.58 ± 2% +71.0% 2.70 ± 2% +26.9% 2.01 ± 2%
> > > > > +33.2% 2.11 reaim.std_dev_percent
> > > > > 0.00 ± 5% +110.4% 0.01 ± 3% +48.8% 0.01 ± 7%
> > > > > +65.3% 0.01 ± 3% reaim.std_dev_time
> > > > > 50800 -2.4% 49600 -1.6% 50000
> > > > > -1.8% 49866 reaim.workload
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Zhengjun Xing
> > >
> > > --
> > > Zhengjun Xing
>
> --
> Zhengjun Xing