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

Vincent Guittot
2020-06-17T16:26:11Z

Le mercredi 17 juin 2020 à 16:57:25 (+0200), Vincent Guittot a écrit :
> 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:
> >
> > =========================================================================================
> > 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
>

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

>
>
> > 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