linux-kernel - Re: [PATCH 4/4] sched,fair: Fix PELT integrity for new tasks

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Date:	Mon, 20 Jun 2016 12:07:04 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Yuyang Du <yuyang.du@...el.com>, Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 4/4] sched,fair: Fix PELT integrity for new tasks

On 20 June 2016 at 11:52, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Jun 20, 2016 at 11:23:39AM +0200, Vincent Guittot wrote:
>
>> > @@ -738,7 +739,20 @@ void post_init_entity_util_avg(struct sc
>> >             sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
>> >     }
>> >
>> > -   update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, false);
>> > +   if (entity_is_task(se)) {
>>
>> Why only task ?
>
> Only tasks can be of another class, the cgroup se's must be fair.

ok

>
>> > +           struct task_struct *p = task_of(se);
>> > +           if (p->sched_class != &fair_sched_class) {
>> > +                   /*
>> > +                    * For !fair tasks do attach_entity_load_avg()
>> > +                    * followed by detach_entity_load_avg() as per
>> > +                    * switched_from_fair().
>> > +                    */
>> > +                   se->avg.last_update_time = now;
>> > +                   return;
>> > +           }
>> > +   }
>> > +
>> > +   update_cfs_rq_load_avg(now, cfs_rq, false);
>> >     attach_entity_load_avg(cfs_rq, se);
>>
>> Don't we have to do a complete attach with attach_task_cfs_rq instead
>> of just the load_avg ? to set also depth ?
>
> init_tg_cfs_entity() sets depth for cgroup entities,
> attach_task_cfs_rq() reset depth on switched_to().
>
> So that should be fine.

But for new fair task ? it will not be set

>
>> ---
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -723,6 +723,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
>>       struct cfs_rq *cfs_rq = cfs_rq_of(se);
>>       struct sched_avg *sa = &se->avg;
>>       long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
>> +     u64 now = cfs_rq_clock_task(cfs_rq);
>>
>>       if (cap > 0) {
>>               if (cfs_rq->avg.util_avg != 0) {
>> @@ -737,8 +738,18 @@ void post_init_entity_util_avg(struct sched_entity *se)
>>               sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
>>       }
>>
>> -     update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, false);
>> -     attach_entity_load_avg(cfs_rq, se);
>
> There is no p here...

yes my condition is just wrong

>
>> +     if (p->sched_class == &fair_sched_class) {
>> +             /* fair entity must be attached to cfs_rq */
>> +             attach_task_cfs_rq(se);
>> +     } else {
>> +             /*
>> +              * For !fair tasks do attach_entity_load_avg()
>> +              * followed by detach_entity_load_avg() as per
>> +              * switched_from_fair().
>> +              */
>> +             se->avg.last_update_time = now;
>> +     }
>> +
>>  }
>
> And you're now not attaching new cgroup thingies.