linux-kernel - Re: [discussion]sched: a rough proposal to enable power saving in scheduler

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Message-ID: <CAKfTPtA98e8GYGwaj4k9y_-4h3e3UOguqJmdkqF0v3Y+5tPRpw@mail.gmail.com>
Date:	Mon, 20 Aug 2012 17:47:29 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	svaidy@...ux.vnet.ibm.com, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in scheduler

On 16 August 2012 07:03, Alex Shi <alex.shi@...el.com> wrote:
> On 08/16/2012 12:19 AM, Matthew Garrett wrote:
>
>> On Mon, Aug 13, 2012 at 08:21:00PM +0800, Alex Shi wrote:
>>
>>> power aware scheduling), this proposal will adopt the
>>> sched_balance_policy concept and use 2 kind of policy: performance, power.
>>
>> Are there workloads in which "power" might provide more performance than
>> "performance"? If so, don't use these terms.
>>
>
>
> Power scheme should no chance has better performance in design.

A side effect of packing small tasks on one core is that you always
use the core with the lowest C-state which will minimize the wake up
latency so you can sometime get better results than performance mode
which will try to use a other core in another cluster which will take
more time to wake up that waiting for the end of the current task.

Vincent
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