linux-kernel - Re: [PATCH 5/7 v4] sched: propagate asynchrous detach

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Date:   Wed, 12 Oct 2016 17:18:29 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Wanpeng Li <kernellwp@...il.com>,
        Yuyang Du <yuyang.du@...el.com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
        Paul Turner <pjt@...gle.com>,
        Benjamin Segall <bsegall@...gle.com>
Subject: Re: [PATCH 5/7 v4] sched: propagate asynchrous detach

On 12/10/16 16:45, Vincent Guittot wrote:
> On 12 October 2016 at 17:03, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>> On 26/09/16 13:19, Vincent Guittot wrote:

[...]

>>> @@ -6607,6 +6609,10 @@ static void update_blocked_averages(int cpu)
>>>
>>>               if (update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, true))
>>>                       update_tg_load_avg(cfs_rq, 0);
>>> +
>>> +             /* Propagate pending load changes to the parent */
>>> +             if (cfs_rq->tg->se[cpu])
>>> +                     update_load_avg(cfs_rq->tg->se[cpu], 0);
>>
>> In my test (1 task (run/period: 8ms/16ms) in tg_root->tg_x->tg_y->*tg_z*
>> and oscillating between cpu1 and cpu2) the cfs_rq related signals are
>> nicely going down to 0 after the task has left the cpu but it doesn't
>> seem to be the case for the corresponding se (cfs_rq->tg->se[cpu])?
> 
> strange because such use case is part of the functional tests that I
> run and it was working fine according to last test that I did
> 
>>
>> It should actually work correctly because of the
>> update_tg_cfs_util/load() calls in update_load_avg(cfs_rq->tg->se[cpu],
>> 0)->propagate_entity_load_avg()
> 
> Furthermore, the update of the parent cfs_rq tg_x->cfs_rq[cpu] uses
> the delta between previous and new value for the child tg_y->se[cpu].
> So it means that if tg_x->cfs_rq[cpu]->avg.load_avg goes down to 0,
> tg_y->se[cpu]->avg.load_avg has at least changed and most probably
> goes down to 0 too

Makes sense.

> 
> Can't it be a misplaced trace point ?

Yes, you're right, it was a missing tracepoint. I only had se and cfs_rq
pelt tracepoints in __update_load_avg() and
attach/detach_entity_load_avg(). I've added them as well to
propagate_entity_load_avg() after the update_tg_cfs_load() call and now
it makes sense. Thanks!

[...]