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Date: Tue, 18 Oct 2016 14:58:28 -0700
From: Joonwoo Park <joonwoop@...eaurora.org>
To: Vincent Guittot <vincent.guittot@...aro.org>,
Peter Zijlstra <peterz@...radead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>,
Joseph Salisbury <joseph.salisbury@...onical.com>,
Ingo Molnar <mingo@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
Mike Galbraith <efault@....de>, omer.akram@...onical.com
Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes
On 10/18/2016 04:56 AM, Vincent Guittot wrote:
> Le Tuesday 18 Oct 2016 à 12:34:12 (+0200), Peter Zijlstra a écrit :
>> On Tue, Oct 18, 2016 at 11:45:48AM +0200, Vincent Guittot wrote:
>>> On 18 October 2016 at 11:07, Peter Zijlstra <peterz@...radead.org> wrote:
>>>> So aside from funny BIOSes, this should also show up when creating
>>>> cgroups when you have offlined a few CPUs, which is far more common I'd
>>>> think.
>>>
>>> The problem is also that the load of the tg->se[cpu] that represents
>>> the tg->cfs_rq[cpu] is initialized to 1024 in:
>>> alloc_fair_sched_group
>>> for_each_possible_cpu(i) {
>>> init_entity_runnable_average(se);
>>> sa->load_avg = scale_load_down(se->load.weight);
>>>
>>> Initializing sa->load_avg to 1024 for a newly created task makes
>>> sense as we don't know yet what will be its real load but i'm not sure
>>> that we have to do the same for se that represents a task group. This
>>> load should be initialized to 0 and it will increase when task will be
>>> moved/attached into task group
>>
>> Yes, I think that makes sense, not sure how horrible that is with the
>
> That should not be that bad because this initial value is only useful for
> the few dozens of ms that follow the creation of the task group
>
>>
>> current state of things, but after your propagate patch, that
>> reinstates the interactivity hack that should work for sure.
>
> The patch below fixes the issue on my platform:
>
> Dietmar, Omer can you confirm that this fix the problem of your platform too ?
I just noticed this thread after posting
https://lkml.org/lkml/2016/10/18/719...
Noticed this bug while a ago and had the patch above at least a week but
unfortunately didn't have time to post...
I think Omer had same problem I was trying to fix and I believe patch I
post should address it.
Vincent, your version fixes my test case as well.
This is sched_stat from the same test case I had in my changelog.
Note dd-2030 which is in root cgroup had same runtime as dd-2033 which
is in child cgroup.
dd (2030, #threads: 1)
-------------------------------------------------------------------
se.exec_start : 275700.024137
se.vruntime : 10589.114654
se.sum_exec_runtime : 1576.837993
se.nr_migrations : 0
nr_switches : 159
nr_voluntary_switches : 0
nr_involuntary_switches : 159
se.load.weight : 1048576
se.avg.load_sum : 48840575
se.avg.util_sum : 19741820
se.avg.load_avg : 1022
se.avg.util_avg : 413
se.avg.last_update_time : 275700024137
policy : 0
prio : 120
clock-delta : 34
dd (2033, #threads: 1)
-------------------------------------------------------------------
se.exec_start : 275710.037178
se.vruntime : 2383.802868
se.sum_exec_runtime : 1576.547591
se.nr_migrations : 0
nr_switches : 162
nr_voluntary_switches : 0
nr_involuntary_switches : 162
se.load.weight : 1048576
se.avg.load_sum : 48316646
se.avg.util_sum : 21235249
se.avg.load_avg : 1011
se.avg.util_avg : 444
se.avg.last_update_time : 275710037178
policy : 0
prio : 120
clock-delta : 36
Thanks,
Joonwoo
>
> ---
> kernel/sched/fair.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8b03fb5..89776ac 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -690,7 +690,14 @@ void init_entity_runnable_average(struct sched_entity *se)
> * will definitely be update (after enqueue).
> */
> sa->period_contrib = 1023;
> - sa->load_avg = scale_load_down(se->load.weight);
> + /*
> + * Tasks are intialized with full load to be seen as heavy task until
> + * they get a chance to stabilize to their real load level.
> + * group entity are intialized with null load to reflect the fact that
> + * nothing has been attached yet to the task group.
> + */
> + if (entity_is_task(se))
> + sa->load_avg = scale_load_down(se->load.weight);
> sa->load_sum = sa->load_avg * LOAD_AVG_MAX;
> /*
> * At this point, util_avg won't be used in select_task_rq_fair anyway
>
>
>
>
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