linux-kernel - Re: [patch v8 4/9] sched: fix slept time double counting in enqueue entity

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Date:	Fri, 21 Jun 2013 21:26:06 +0800
From:	Lei Wen <adrian.wenl@...il.com>
To:	Alex Shi <seakeel@...il.com>
Cc:	Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>,
	Changlong Xie <changlongx.xie@...el.com>, sgruszka@...hat.com,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [patch v8 4/9] sched: fix slept time double counting in enqueue entity

On Fri, Jun 21, 2013 at 7:09 PM, Alex Shi <seakeel@...il.com> wrote:
>
>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>> index c61a614..9640c66 100644
>>>> --- a/kernel/sched/fair.c
>>>> +++ b/kernel/sched/fair.c
>>>> @@ -5856,7 +5856,8 @@ static void switched_from_fair(struct rq *rq,
>>>> struct task_struct *p)
>>>>         */
>>>>         if (p->se.avg.decay_count) {
>>>>                 struct cfs_rq *cfs_rq = cfs_rq_of(&p->se);
>>>> -               __synchronize_entity_decay(&p->se);
>>>> +               p->se.avg.last_runnable_update +=
>>>> +                               __synchronize_entity_decay(&p->se);
>>>
>>> it is not needed, since the last_runnable_update will be reset if it
>>> will be switched to fair.
>>
>> When it is backed to fair class, the only thing scheduler would do
>> is to check whether it could preempt current running task, so
>> where to reset the last_runnable_update?
>
> here, when the task enqueue to cfs_rq.
> avg.decay_count == 0, so the last line will reset last_runnable_update.
>
> Anyway, you may consider to add a comment in the function, since it is bit hard
> to understand for you.
>
> ---
> /* Add the load generated by se into cfs_rq's child load-average */
> static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
>                                                   struct sched_entity *se,
>                                                   int wakeup)
> {
>         /*
>          * We track migrations using entity decay_count <= 0, on a wake-up
>          * migration we use a negative decay count to track the remote decays
>          * accumulated while sleeping.
>          */
>         if (unlikely(se->avg.decay_count <= 0)) {
>                 se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task;


I see...
I didn't notice before the switched_from_fair, we already called
dequeue and enqueue.
Since it works as expected, I have no question.

Thanks for your detailed explanation! :)

Thanks,
Lei

>
>>
>> Thanks,
>> Lei
>>
>>>
>>> --
>>> Thanks
>>>     Alex
>
>
> --
> Thanks
>     Alex
--
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