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Message-ID: <20090428085237.GB26487@elte.hu>
Date: Tue, 28 Apr 2009 10:52:37 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: 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>,
Dipankar Sarma <dipankar@...ibm.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Vatsa <vatsa@...ux.vnet.ibm.com>,
Gautham R Shenoy <ego@...ibm.com>,
Andi Kleen <andi@...stfloor.org>,
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 v1 0/3] Saving power by cpu evacuation using
sched_mc=n
* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > > Also, the user interface should be that single thermal
> > > capacity knob, more fine grained control is undesired.
> >
> > For power savings, a single evacuation knob will do. While for
> > thermal we will need additional parameters to choose the right
> > cores to evacuate. Some sort of directional/vector parameter.
>
> Why? are machines that non-uniform in cooling capacity that it
> really matters which core generates the heat? Sounds like badly
> designed hardware to me.
>
> I would expect it to only be the total head generated/power taken
> from the rack unit.
If we add thermal throttling at the kernel level then a single knob
(with a percentile-ish unit) is probably the furthest we will go -
with "not doing it at all" still being the other, very tempting
alternative.
If the only technical way you can find to do it is via myriads of
non-intuitive knobs and per core settings - then the answer is
really 'no thanks'.
Ingo
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