linux-kernel - Re: [RFC/PATCH] sched: Honor sync wake up in select_idle

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Message-ID: <87boijw2mp.fsf@sejong.aot.lge.com>
Date:	Fri, 10 Aug 2012 17:51:58 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Mike Galbraith <efault@....de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [RFC/PATCH] sched: Honor sync wake up in select_idle_sibling

Hi, Mike

On Fri, 10 Aug 2012 10:14:44 +0200, Mike Galbraith wrote:
> On Fri, 2012-08-10 at 16:25 +0900, Namhyung Kim wrote: 
>> From: Namhyung Kim <namhyung.kim@....com>
>> 
>> When sync wakeup happens and there's the waker task running alone,
>> select the target cpu as if it's already idle.
>
> Ouch.  That defeats the purpose of select_idle_sibling().  Just because
> we're doing a sync wakeup does not mean there's no convertible overlap,
> nor that the waker is really really going to take a nap immediately.  A
> lot of the places that benefit up to and including hugely from looking
> for an idle shared cache to wake to do sync wakeups.

Thanks for the explanation! I misunderstood the function ;)

Thanks,
Namhyung

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