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

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Message-ID: <20120817184705.GB13369@srcf.ucam.org>
Date:	Fri, 17 Aug 2012 19:47:05 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	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 11:44:03AM -0700, Arjan van de Ven wrote:
> On 8/17/2012 11:41 AM, Matthew Garrett wrote:
> > On Thu, Aug 16, 2012 at 07:01:25AM -0700, Arjan van de Ven wrote:
> >> this is ... a dubiously general statement.
> >>
> >> for good power, at least on Intel cpus, you want to spread. Parallelism is efficient.
> > 
> > Is this really true? In a two-socket system I'd have thought the benefit 
> > of keeping socket 1 in package C3 outweighed the cost of keeping socket 
> > 0 awake for slightly longer.
> 
> not on Intel
> 
> you can't enter package c3 either until every one is down.
> (e.g. memory controller must stay on etc etc)

I thought that was only PC6 - is there any reason why the package cache 
can't be entirely powered down?

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