linux-kernel - Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE

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Date:	Wed, 03 Jun 2015 17:30:44 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Rik van Riel <riel@...hat.com>, Josef Bacik <jbacik@...com>,
	mingo@...hat.com, linux-kernel@...r.kernel.org,
	morten.rasmussen@....com, kernel-team <Kernel-team@...com>
Subject: Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for
 BALANCE_WAKE

On Wed, 2015-06-03 at 16:24 +0200, Peter Zijlstra wrote:
> On Wed, 2015-06-03 at 10:12 -0400, Rik van Riel wrote:
> 
> > There is a policy vs mechanism thing here. Ingo and Peter
> > are worried about the overhead in the mechanism of finding
> > an idle CPU.  Your measurements show that the policy of
> > finding an idle CPU is the correct one.
> 
> For his workload; I'm sure I can find a workload where it hurts.
> 
> In fact, I'm fairly sure Mike knows one from the top of his head, seeing
> how he's the one playing about trying to shrink that idle search :-)

Like anything where scheduling latency doesn't heavily dominate.  Even
if searching were free, bounces aren't, even for the very light.

	-Mike

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