linux-kernel - Re: Plumbers: Tweaking scheduler policy micro-conf RFP

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Message-ID: <54348.1337113582@turing-police.cc.vt.edu>
Date:	Tue, 15 May 2012 16:26:22 -0400
From:	valdis.kletnieks@...edu
To:	Pantelis Antoniou <pantelis.antoniou@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	mou Chen <hi3766691@...il.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, torvalds@...ux-foundation.org
Subject: Re: Plumbers: Tweaking scheduler policy micro-conf RFP

On Tue, 15 May 2012 14:35:53 +0300, Pantelis Antoniou said:

> Thermal management: How to distribute load to the processors in such
> a way that the temperature of the die doesn't increase too much that
> we have to either go to a lower OPP or shut down the core all-together.
> This is in direct conflict with throughput since we'd have better performance
> if we could keep the same warmed-up cpu going.

It's not just "temperature of the die".  When you have multiple aisles of 42U
racks full of servers, you often hit "must keep average total BTU load per
server below X" constraints.  There's plenty of colo's that are only using 40%
of their floor space due to cooling constraints (you may be able to get the
power company to pull another megawatt of copper into the building, but then
you need to find someplace to put another megawatt worth of cooling).

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