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SubjectRe: [PATCH] sched: Get rid of unnecessary checks from select_idle_sibling
On 01/09/2013 03:54 PM, Namhyung Kim wrote:
> Hi Alex,
>
> On Wed, 09 Jan 2013 15:33:40 +0800, Alex Shi wrote:
>> On 01/09/2013 02:50 PM, Namhyung Kim wrote:
>>> From: Namhyung Kim <namhyung.kim@lge.com>
>>>
>>> AFAICS @target cpu of select_idle_sibling() is always either prev_cpu
>>> or this_cpu. So no need to check it again and the conditionals can be
>>> consolidated.
> [snip]
>> Uh, we don't know if the target is this_cpu or previous cpu, If we just
>> check the target idle status, we may miss another idle cpu. So this
>> patch change the logical in this function.
>
> select_idle_sibling() is called only in select_task_rq_fair() if it
> found a suitable affine_sd. The default target is the 'prev_cpu' of the
> task but if wake_affine() returns true it'd be (this) 'cpu'.
>
> I cannot see where the prev_cpu or the cpu is set to another one before
> calling select_idle_sibling.

The old logical will return directly whenever prev_cpu or this cpu idle,
but your new logical just has one chance.


>
> Thanks,
> Namhyung
>


--
Thanks Alex


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