From: Alex Shi <alex.shi@intel.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
LKML <linux-kernel@vger.kernel.org>,
Namhyung Kim <namhyung.kim@lge.com>,
Mike Galbraith <efault@gmx.de>,
Preeti U Murthy <preeti@linux.vnet.ibm.com>,
Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH] sched: Get rid of unnecessary checks from select_idle_sibling
Date: Wed, 09 Jan 2013 16:34:39 +0800 [thread overview]
Message-ID: <50ED2B9F.3080800@intel.com> (raw)
In-Reply-To: <876236rdum.fsf@sejong.aot.lge.com>
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
next prev parent reply other threads:[~2013-01-09 8:33 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-09 6:50 [PATCH] sched: Get rid of unnecessary checks from select_idle_sibling Namhyung Kim
2013-01-09 7:33 ` Alex Shi
2013-01-09 7:38 ` Alex Shi
2013-01-09 8:00 ` Namhyung Kim
2013-01-09 7:54 ` Namhyung Kim
2013-01-09 8:34 ` Alex Shi [this message]
2013-01-10 5:52 ` Namhyung Kim
2013-01-11 2:36 ` Alex Shi
2013-01-09 8:21 ` Preeti U Murthy
2013-01-10 5:49 ` Namhyung Kim
2013-01-10 8:19 ` Preeti U Murthy
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