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

Vincent Guittot
2020-06-18T12:35:53Z

On Thu, 18 Jun 2020 at 04:45, Xing Zhengjun
<zhengjun.xing@linux.intel.com> wrote:
>
>
>

> >>
> >> 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
> >>
> >
> > The patch above tries to move back to the group in the same classification as
> > before but this could harm other benchmarks.
> >
> > There is another way to fix this by easing the migration of task in the case
> > of migrate_util imbalance.
> >
> > Could you also try the patch below instead of the one above ?
> >
> > ---
> > kernel/sched/fair.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 0aeffff62807..fcaf66c4d086 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7753,7 +7753,8 @@ static int detach_tasks(struct lb_env *env)
> > case migrate_util:
> > util = task_util_est(p);
> >
> > - if (util > env->imbalance)
> > + if (util/2 > env->imbalance &&
> > + env->sd->nr_balance_failed <= env->sd->cache_nice_tries)
> > goto next;
> >
> > env->imbalance -= util;
> > --
> > 2.17.1
> >
> >
>
> 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
> 69c81543653bf5f2c7105086502889fa019c15cb (the test patch)
>
> 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2 v5.7
> 69c81543653bf5f2c7105086502
> ---------------- --------------------------- ---------------------------
> ---------------------------
> %stddev %change %stddev %change
> %stddev %change %stddev
> \ | \ | \
> | \
> 0.69 -10.3% 0.62 -9.1% 0.62
> -7.6% 0.63 reaim.child_systime
> 0.62 -1.0% 0.61 +0.5% 0.62
> +1.9% 0.63 reaim.child_utime
> 66870 -10.0% 60187 -7.6% 61787
> -5.9% 62947 reaim.jobs_per_min

There is an improvement but not at the same level as on my setup.
I'm not sure with patch you tested here. Is it the last one that
modify detach_tasks() or the previous one that modify
post_init_entity_util_avg() ?

Could you also try the other one ? Both patches were improving results
on y setup but the behavior doesn't seem to be the same on your setup.

> 16717 -10.0% 15046 -7.6% 15446
> -5.9% 15736 reaim.jobs_per_min_child
> 97.84 -1.1% 96.75 -0.4% 97.43
> -0.4% 97.47 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
> +6.0% 0.38 reaim.parent_time
> 1.58 ± 2% +71.0% 2.70 ± 2% +26.9% 2.01 ±
> 2% +23.6% 1.95 ± 3% reaim.std_dev_percent
> 0.00 ± 5% +110.4% 0.01 ± 3% +48.8% 0.01 ±
> 7% +43.2% 0.01 ± 5% reaim.std_dev_time
> 50800 -2.4% 49600 -1.6% 50000
> -0.8% 50400 reaim.workload
>
>
> >>
> >>
...
> >>>>>
> >>>>> --
> >>>>> Zhengjun Xing
> >>>
> >>> --
> >>> Zhengjun Xing
>
> --
> Zhengjun Xing