linux-kernel - Re: [PATCH 2/3] sched: Move idle_balance() to post

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Date:	Wed, 13 Feb 2013 19:43:01 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH 2/3] sched: Move idle_balance() to post_schedule

On Tue, 2013-02-12 at 17:54 -0500, Steven Rostedt wrote:
> There's no real reason that the idle_balance() needs to be called in
> the
> middle of schedule anyway. The only benefit is that if a task is
> pulled
> to this CPU, it can be scheduled without the need to schedule the idle
> task. 

Uhm, istr that extra schedule being an issue somewhere.. Make very sure
you don't regress anything silly like sysbench or hackbench. Maybe ask
Mike, he seems to have a better retention for benchmark weirdness than
me.

> But load balancing and migrating the task makes a switch to idle
> and back negligible.

How does that follow? We can have to-idle switches _far_ more often than
we balance.

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