linux-kernel - Re: [RFC PATCH 06/16] arm: topology: Define TC2 sched energy and provide it to scheduler

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Date:	Mon, 9 Jun 2014 09:27:39 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Yuyang Du <yuyang.du@...el.com>,
	Dirk Brandewie <dirk.brandewie@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>
Subject: Re: [RFC PATCH 06/16] arm: topology: Define TC2 sched energy and
 provide it to scheduler

On Sat, Jun 07, 2014 at 03:33:58AM +0100, Nicolas Pitre wrote:
> On Fri, 6 Jun 2014, Ingo Molnar wrote:
> 
> > In any case, even with turbo frequencies, switching power use is 
> > probably an order of magnitude higher than leakage current power use, 
> > on any marketable chip, so we should concentrate on being able to 
> > cover this first order effect (P/work ~ V^2), before considering any 
> > second order effects (leakage current).
> 
> Just so that people are aware... We'll have to introduce thermal 
> constraint management into the scheduler mix as well at some point.  
> Right now what we have is an ad hoc subsystem that simply monitors 
> temperature and apply crude cooling strategies when some thresholds are 
> met. But a better strategy would imply thermal "provisioning".

There is already work going on to improve thermal management:

http://lwn.net/Articles/599598/

The proposal is based on power/energy models (too). The goal is to
allocate power intelligently based on performance requirements.

While it is related to energy-aware scheduling and I fully agree that it
is something we need to consider, I think it is worth developing the two
ideas in parallel and look at sharing things like the power model later
once things mature. Energy-aware scheduling is complex enough on its
own to keep us entertained for a while :-)

Morten
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