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SubjectRe: [PATCH] sched/fair: Optimize dequeue_task_fair()
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On 6/15/20 11:09 PM, Vincent Guittot wrote:
> On Mon, 15 Jun 2020 at 16:20, Peng Wang <rocking@linux.alibaba.com> wrote:
>>
>> While looking at enqueue_task_fair and dequeue_task_fair, it occurred
>> to me that dequeue_task_fair can also be optimized as Vincent described
>> in commit 7d148be69e3a ("sched/fair: Optimize enqueue_task_fair()").
>
> good point
>
>>
>> dequeue_throttle label can ensure se not to be NULL, and se is
>> always NULL when reaching root level.
>>
>> Signed-off-by: Peng Wang <rocking@linux.alibaba.com>
>> ---
>> kernel/sched/fair.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index cbcb2f7..e6be952 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5614,10 +5614,10 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>>
>> }
>>
>> -dequeue_throttle:
>> - if (!se)
>> - sub_nr_running(rq, 1);
>> + /* At this point se is NULL and we are at root level*/
>> + sub_nr_running(rq, 1);
>>
>> +dequeue_throttle:
>> /* balance early to pull high priority tasks */
>> if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
>> rq->next_balance = jiffies;
>
> You can move the label here because sched_idle_rq() uses
> rq->nr-running and rq->cfs.idle_h_nr_running so they will not change
> if we jump to the label before reaching root level

Yes, then we can also skip the early balance check.

>
>> --
>> 2.9.5
>>

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