linux-kernel - Re: [RFC PATCH v2 0/2] Saving power by cpu evacuation sched_max_capacity

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Message-ID: <20090513144659.GV19296@one.firstfloor.org>
Date:	Wed, 13 May 2009 16:46:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arun Bharadwaj <arun@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH v2 0/2] Saving power by cpu evacuation sched_max_capacity_pct=n

On Wed, May 13, 2009 at 04:36:42PM +0200, Peter Zijlstra wrote:
> On Wed, 2009-05-13 at 16:35 +0200, Andi Kleen wrote:
> > On Wed, May 13, 2009 at 06:41:00PM +0530, Vaidyanathan Srinivasan wrote:
> > > * Using sched_mc=3,4,5 to evacuate 1,2,4 cores is completely
> > >   non-intuitive and broken interface.  Ingo wanted to see if we can
> > >   model a global percentile tunable that would map to core throttling.
> > 
> > I have one request. CPU throttling is already a very well established
> > term in the x86 world, refering to thermal throttling when the CPU
> > overheats. This is implemented by ACPI and the CPU. It's always
> > a very bad thing that should be avoided at all costs.
> 
> Its about avoiding that.

Hmm? Can you explain please? CPU throttling should only happen when your
cooling system is broken in some way.

It's not a power saving feature, just a "don't make CPU melt" feature.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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