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

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Message-ID: <20120817195033.GA15589@srcf.ucam.org>
Date:	Fri, 17 Aug 2012 20:50:34 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Chris Friesen <chris.friesen@...band.com>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	preeti <preeti@...ux.vnet.ibm.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,
	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>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in
 scheduler

On Fri, Aug 17, 2012 at 01:45:09PM -0600, Chris Friesen wrote:
> On 08/17/2012 12:47 PM, Matthew Garrett wrote:

> The datasheet for the Xeon E5 (my variant at least) says it doesn't
> do C7 so never powers down the LLC.  However, as you said earlier
> once you can put the socket into C6 which saves about 30W compared
> to C1E.
> 
> So as far as I can see with this CPU at least you would benefit from
> shutting down a whole socket when possible.

Having any active cores on the system prevents all packages from going 
into PC6 or deeper. What I'm not clear on is whether less deep package C 
states are also blocked.

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