linux-kernel - Re: [PATCH] sched: fix sched_entity avg statistics update

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Date:	Tue, 21 Jan 2014 21:06:19 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Benjamin Segall <bsegall@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH] sched: fix sched_entity avg statistics update

On 21 January 2014 19:38,  <bsegall@...gle.com> wrote:
> Vincent Guittot <vincent.guittot@...aro.org> writes:
>
>> 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.
>
> ... Gah, that's correct, we had this right the first time. Could you do
> this as a full revert of 282cf499f03ec1754b6c8c945c9674b02631fb0f (ie
> remove the now inaccurate comment, or maybe replace it with a correct one).

Ok i'm going to remove comment as well and replace it with a new description

Vincent

>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> ---
>>  kernel/sched/fair.c |    3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index e64b079..5b0ef90 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -2370,8 +2370,7 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
>>                * 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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