Message-ID: <1345640993.26849.62.camel@marge.simpson.net>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in
 scheduler
From: Mike Galbraith <efault@gmx.de>
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Ingo Molnar <mingo@kernel.org>,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Alex Shi <alex.shi@intel.com>,
        Suresh Siddha <suresh.b.siddha@intel.com>, vincent.guittot@linaro.org,
        svaidy@linux.vnet.ibm.com, Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Paul Turner <pjt@google.com>
Date: Wed, 22 Aug 2012 15:09:53 +0200
In-Reply-To: <5034D878.1000305@linux.intel.com>
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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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