linux-kernel - Re: RFC: A proposal for power capping through forced idle in the Linux Kernel

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Message-ID: <20091222205743.4b6cf677@infradead.org>
Date:	Tue, 22 Dec 2009 20:57:43 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Salman Qazi <sqazi@...gle.com>, linux-kernel@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Rubin <mrubin@...gle.com>,
	Taliver Heath <taliver@...gle.com>
Subject: Re: RFC: A proposal for power capping through forced idle in the
 Linux  Kernel

On Tue, 22 Dec 2009 20:48:24 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, 2009-12-14 at 16:19 -0800, Arjan van de Ven wrote:
> 
> > I like the general idea, I have one request (that I didn't see
> > quite in your explanation): Please make sure that all cpus in the
> > system do their idle injection at the same time, so that memory can
> > go into power saving mode as well during this time etc etc...
> 
> And then you're going to ask that it scales too, right? :-)
> 
> Gang-scheduling is inherently non scalable, be it for idle time or
> not.

well... there's many ways to do this... one option is to agree, ahead
of time, which jiffies values you're going to do the idle thing on.
Say every 100 jiffies where jiffies % 100 is 0....

then the scalability thing isn't a big deal.. and you still do it all
at the same time. Or at least "enough" at the same time for it to not
matter



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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