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SubjectRe: [PATCH RFC v2] sched/fair: simplify the work when reweighting entity(Internet mail)
Date
Hi,

> On Aug 11, 2020, at 5:50 PM, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>
> On 06/08/2020 18:14, Jiang Biao wrote:
>> From: Jiang Biao <benbjiang@tencent.com>
>>
>> If a se is on_rq when reweighting entity, all we need should be
>> updating the load of cfs_rq, other dequeue/enqueue work could be
>> redundant, such as,
>> * nr_running--/nr_running++
>>
>> Even though the following dequeue/enqueue path would never be reached
>> * account_numa_dequeue/account_numa_enqueue
>> * list_del/list_add from/into cfs_tasks
>> but it could be a little confusing.
>>
>> Simplifying the logic could be helpful to reduce a litte overhead for
>> hot path, and make it cleaner and more readable.
>
> LGTM. I guess you have to resend it w/o the RFC tag.
Will do soon.
>
> Maybe you can rework the patch header a little?
>
> Something like this:
>
> The code in reweight_entity() can be simplified.
>
> For a sched entity on the rq, the entity accounting can be replaced by
> cfs_rq instantaneous load updates currently called from within the
> entity accounting.
>
> Even though an entity on the rq can't represent a task in
> reweight_entity() (a task is always dequeued before calling this
> function) and so the numa task accounting and the rq->cfs_tasks list
> management of the entity accounting are never called, the redundant
> cfs_rq->nr_running decrement/increment will be avoided.
That’s a much better. I’ll pick the header if you don’t mind. :)

Thanks a lot for your kindly reply and detailed explanation.

Regards,
Jiang
>
>>
>> Signed-off-by: Jiang Biao <benbjiang@tencent.com>
>> ---
>> v2<-v1:
>> - Amend the commit log.
>>
>> kernel/sched/fair.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 04fa8dbcfa4d..18a8fc7bd0de 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3086,7 +3086,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>> /* commit outstanding execution time */
>> if (cfs_rq->curr == se)
>> update_curr(cfs_rq);
>> - account_entity_dequeue(cfs_rq, se);
>> + update_load_sub(&cfs_rq->load, se->load.weight);
>> }
>> dequeue_load_avg(cfs_rq, se);
>>
>> @@ -3102,7 +3102,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>>
>> enqueue_load_avg(cfs_rq, se);
>> if (se->on_rq)
>> - account_entity_enqueue(cfs_rq, se);
>> + update_load_add(&cfs_rq->load, se->load.weight);
>>
>> }

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