linux-kernel - Re: [PATCH] sched: wake up task on prev_cpu if not in SD_WAKE

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Message-ID: <536D1B6D.8060004@redhat.com>
Date:	Fri, 09 May 2014 14:16:13 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, morten.rasmussen@....com,
	mingo@...nel.org, george.mccollister@...il.com,
	ktkhai@...allels.com
Subject: Re: [PATCH] sched: wake up task on prev_cpu if not in SD_WAKE_AFFINE
 domain with cpu

On 05/09/2014 01:55 PM, Mike Galbraith wrote:
> On Fri, 2014-05-09 at 11:24 -0400, Rik van Riel wrote:
>> On 05/09/2014 11:24 AM, Mike Galbraith wrote:
>
>>> If no ->flags & SD_BALANCE_WAKE is encountered during traversal, sd
>>> remains NULL, we fall through to return prev_cpu.
>      ^^^^^^^^^^^^
>
>> We do fall through, but into this loop:
>
>>           while (sd) {

You are right. That code is a little hard to follow...

That leaves the big question: do we want to fall back to
prev_cpu if it is not idle, and it has an idle sibling,
or would it be better to find an idle sibling of prev_cpu
when we wake up a task?

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