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

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Message-ID: <20120822113508.GA19152@srcf.ucam.org>
Date:	Wed, 22 Aug 2012 12:35:08 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	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, Aug 22, 2012 at 11:10:13AM +0200, Ingo Molnar wrote:
> 
> * Matthew Garrett <mjg59@...f.ucam.org> wrote:
> 
> > [...]
> >
> > Our power consumption is worse than under other operating 
> > systems is almost entirely because only one of our three GPU 
> > drivers implements any kind of useful power management. [...]
> 
> ... and because our CPU frequency and C state selection logic is 
> doing pretty much the worst possible decisions (on x86 at 
> least).

You have figures showing that our C state residence is worse than, say, 
Windows? Because my own testing says that we're way better at that. 
Could we be better? Sure. Is it why we're worse? No.

> Regardless, you cannot possibly seriously suggest that because 
> there's even greater suckage elsewhere for some workloads we 
> should not even bother with improving the situation here.

I'm enthusiastic about improving the scheduler's behaviour. I'm 
unenthusiastic about putting in automatic hacks related to AC state.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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