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

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Date:	Wed, 22 Aug 2012 15:09:53 +0200
From:	Mike Galbraith <efault@....de>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...nel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Alex Shi <alex.shi@...el.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	vincent.guittot@...aro.org, svaidy@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in
 scheduler

On Wed, 2012-08-22 at 06:02 -0700, Arjan van de Ven wrote: 
> On 8/21/2012 10:41 PM, Mike Galbraith wrote:
> > On Tue, 2012-08-21 at 17:02 +0100, Alan Cox wrote:
> > 
> >> I'd like to see actual numbers and evidence on a wide range of workloads
> >> the spread/don't spread thing is even measurable given that you've also
> >> got to factor in effects like completing faster and turning everything
> >> off. I'd *really* like to see such evidence on a laptop,which is your
> >> one cited case it might work.
> > 
> > For my dinky dual core laptop, I suspect you're right, but for a more
> > powerful laptop, I'd expect spread/don't to be noticeable.
> 
> yeah if you don't spread, you will waste some power.
> but.. current linux behavior is to spread.
> so we can only make it worse.

Hm, so I can stop fretting about select_idle_sibling().  Good. 

> > Yeah, hard numbers would be nice to see.
> > 
> > If I had a powerful laptop, I'd kill irq balancing, and all but periodic
> > load balancing, and expect to see a positive result. 
> 
> I'd expect to see a negative result ;-)

Ok, so I have my head on backward.  Gives a different perspective :)

-Mike

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