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

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Date:	Wed, 11 Jun 2014 12:42:18 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Eduardo Valentin <edubezval@...il.com>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	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 Wed, Jun 11, 2014 at 12:02:51PM +0100, Eduardo Valentin wrote:
> Hello,
> 
> On Mon, Jun 09, 2014 at 09:22:49AM -0400, Nicolas Pitre wrote:
> > On Mon, 9 Jun 2014, Morten Rasmussen wrote:
> > 
> > > 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
> 
> Can you please point me to the other piece of code which is using
> power/energy models too?  We are considering having these models within
> the thermal software compoenents. But if we already have more than one
> user, might be worth considering a separate API.

The link above is to the thermal management proposal which includes a
power model. This one might work better:

http://article.gmane.org/gmane.linux.power-management.general/45000

The power/energy model in this energy-aware scheduling proposal is
different. An example of the model data is in patch 6 (the start of this
thread) and the actual use of the model is in patch 11 and the following
patches. As said below, the two proposals are independent, but there
might be potential for merging the power/energy models once the
proposals are more mature.

Morten

>  
> > > allocate power intelligently based on performance requirements.
> > 
> > Ah, great!  I missed that.
> > 
> > > 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 :-)
> > 
> > Absolutely.  This is why I said "at some point".
> > 
> > 
> > Nicolas
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