linux-kernel - Re: [PATCH RFC] sched/fair: let cpu's cfs

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Date:	Fri, 8 Apr 2016 08:05:15 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Dietmar Eggemann <dietmar.eggemann@....com>
Cc:	Morten Rasmussen <morten.rasmussen@....com>,
	Yuyang Du <yuyang.du@...el.com>, Leo Yan <leo.yan@...aro.org>,
	Steve Muckle <steve.muckle@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"eas-dev@...ts.linaro.org" <eas-dev@...ts.linaro.org>
Subject: Re: [PATCH RFC] sched/fair: let cpu's cfs_rq to reflect task migration

On 7 April 2016 at 22:30, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
> Hi  Vincent,
>
> On 04/07/2016 02:04 PM, Vincent Guittot wrote:
>>
>> Hi Dietmar,
>>
>> On 6 April 2016 at 20:53, Dietmar Eggemann <dietmar.eggemann@....com>
>> wrote:
>>>
>>> On 06/04/16 09:37, Morten Rasmussen wrote:
>>>>
>>>> On Tue, Apr 05, 2016 at 06:00:40PM +0100, Dietmar Eggemann wrote:
>
>
> [...]
>
>>> @@ -2910,8 +2920,13 @@ static void attach_entity_load_avg(struct cfs_rq
>>> *cfs_rq, struct sched_entity *s
>>>          if (!entity_is_task(se))
>>>                  return;
>>>
>>> -       rq_of(cfs_rq)->cfs.avg.util_avg += se->avg.util_avg;
>>> -       rq_of(cfs_rq)->cfs.avg.util_sum += se->avg.util_sum;
>>> +       if (&rq_of(cfs_rq)->cfs == cfs_rq) {
>>> +               rq_of(cfs_rq)->cfs.avg.util_avg += se->avg.util_avg;
>>> +               rq_of(cfs_rq)->cfs.avg.util_sum += se->avg.util_sum;
>>> +       } else {
>>> +               rq_of(cfs_rq)->cfs.added_util_avg = se->avg.util_avg;
>>> +               rq_of(cfs_rq)->cfs.added_util_sum = se->avg.util_sum;
>>> +       }
>>>   }
>>
>>
>> Don't you also need similar thing for the detach ?
>
>
> Maybe? I ran workloads in tg's and checked last_update_time of cfs_rq
> and &rq_of(cfs_rq)->cfs and they always were in sync. That's obviously
> only the call-stack 'task_move_group_fair() -> detach_task_cfs_rq() ->
> detach_entity_load_avg()' and not the one starting from
> switched_from_fair().
>
> [...]
>
>>> But attach_entity_load_avg() is not only called in
>>> enqueue_entity_load_avg() for migrated
>>> tasks but also in attach_task_cfs_rq() which is called from
>>> switched_to_fair() and
>>> task_move_group_fair() where we can't assume that after the
>>> enqueue_entity_load_avg() a
>>> call to update_cfs_rq_load_avg() follows like in
>>>
>>> enqueue_task_fair():
>>>
>>>      for_each_sched_entity(se)
>>>          enqueue_entity()
>>>              enqueue_entity_load_avg()
>>>                      update_cfs_rq_load_avg(now, cfs_rq)
>>>                      if (migrated) attach_entity_load_avg()
>>>
>>>      for_each_sched_entity(se)
>>>          update_load_avg()
>>>              update_cfs_rq_load_avg(now, cfs_rq)
>>>
>>>
>>> Not sure if we can just update the root cfs_rq to
>>> se->avg.last_update_time before we add
>>> se->avg.util_[avg/sum] to rq_of(cfs_rq)->cfs.avg.util_[avg/sum] in
>>> attach_entity_load_avg()?
>>>
>>> cfs_rq throttling has to be considered as well ...
>>
>>
>> IIUC this new proposal, the utilization of a task will be accounted on
>> the utilization of the root cfs_rq thanks  to
>> tsk->se->cfs_rq->tg->se[cpu]->... down to the root cfs_rq. Then, you
>> directly add the utilization of the newly enqueued task in the root
>> cfs_rq.
>
>
> Not sure if you're referring to this, but in __update_load_avg() I
> suppress the utilization update for se's w/ !entity_is_task(se) and
> cfs_rq's w/ &rq_of(cfs_rq)->cfs != cfs_rq  so preventing the first case.

ok, so you still need part of the previous patch, i thought you had
skipped it as it was wrong

>
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