linux-kernel - Re: [PATCH v2] sched: Fast idling of CPU when system is partially loaded

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Date:	Sun, 22 Jun 2014 21:33:08 -0700
From:	Jason Low <jason.low2@...com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Davidlohr Bueson <davidlohr@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: Fast idling of CPU when system is partially
 loaded

On Mon, 2014-06-16 at 12:48 -0700, Tim Chen wrote:

> Thanks to the review from Jason and Peter.  I've moved the check
> of whether load balance is required into fair.c's idle_balance.
> 
> When a system is lightly loaded (i.e. no more than 1 job per cpu),
> attempt to pull job to a cpu before putting it to idle is unnecessary and
> can be skipped.  This patch adds an indicator so the scheduler can know
> when there's no more than 1 active job is on any CPU in the system to
> skip needless job pulls.

> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>

Acked-by: Jason Low <jason.low2@...com>

This change would address one of the main issues I've also been seeing
on my test machines with idle_balance where most of the
find_busiest_group overhead is not useful due to that issue with no
tasks to move.

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