linux-kernel - Re: [PATCH] Revert "sched: Fix sleep time double accounting in enqueue entity"

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Date:	Wed, 22 Jan 2014 11:54:39 -0800
From:	Paul Turner <pjt@...gle.com>
To:	Benjamin Segall <bsegall@...gle.com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Alex Shi <alex.shi@...aro.org>,
	Linaro Kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH] Revert "sched: Fix sleep time double accounting in
 enqueue entity"

On Wed, Jan 22, 2014 at 9:53 AM,  <bsegall@...gle.com> wrote:
> Vincent Guittot <vincent.guittot@...aro.org> writes:
>
>> This reverts commit 282cf499f03ec1754b6c8c945c9674b02631fb0f.
>>
>> With the current implementation, the load average statistics of a sched entity
>> change according to other activity on the CPU even if this activity is done
>> between the running window of the sched entity and have no influence on the
>> running duration of the task.
>>
>> When a task wakes up on the same CPU, we currently update last_runnable_update
>> with the return  of __synchronize_entity_decay without updating the
>> runnable_avg_sum and runnable_avg_period accordingly. In fact, we have to sync
>> the load_contrib of the se with the rq's blocked_load_contrib before removing
>> it from the latter (with __synchronize_entity_decay) but we must keep
>> last_runnable_update unchanged for updating runnable_avg_sum/period during the
>> next update_entity_load_avg.
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> Unless paul wants to squash this into a possible change to the if
> (wakeup) stuff:
> Reviewed-by: Ben Segall <bsegall@...gle.com>
>

I can send that separately as Vincent suggests.  This is good to go.

>>
>> ---
>>  kernel/sched/fair.c |    8 +-------
>>  1 file changed, 1 insertion(+), 7 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index e64b079..6d61f20 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -2365,13 +2365,7 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
>>               }
>>               wakeup = 0;
>>       } else {
>> -             /*
>> -              * Task re-woke on same cpu (or else migrate_task_rq_fair()
>> -              * would have made count negative); we must be careful to avoid
>> -              * double-accounting blocked time after synchronizing decays.
>> -              */
>> -             se->avg.last_runnable_update += __synchronize_entity_decay(se)
>> -                                                     << 20;
>> +             __synchronize_entity_decay(se);
>>       }
>>
>>       /* migrated tasks did not contribute to our blocked load */
--
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