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Date: Wed, 13 May 2009 16:46:59 +0200
From: Andi Kleen <andi@firstfloor.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andi Kleen <andi@firstfloor.org>,
       Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Suresh B Siddha <suresh.b.siddha@intel.com>,
       Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>,
       Arjan van de Ven <arjan@infradead.org>, Ingo Molnar <mingo@elte.hu>,
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       Mike Galbraith <efault@gmx.de>, Thomas Gleixner <tglx@linutronix.de>,
       Arun Bharadwaj <arun@linux.vnet.ibm.com>
Subject: Re: [RFC PATCH v2 0/2] Saving power by cpu evacuation sched_max_capacity_pct=n
Message-ID: <20090513144659.GV19296@one.firstfloor.org>
References: <20090513130541.21440.33364.stgit@drishya.in.ibm.com> <20090513143550.GU19296@one.firstfloor.org> <1242225402.26820.23.camel@twins>
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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@linux.intel.com -- Speaking for myself only.