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 07:43:26 -0400
From:	Eduardo Valentin <edubezval@...il.com>
To:	Morten Rasmussen <morten.rasmussen@....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 12:42:18PM +0100, Morten Rasmussen wrote:
> 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,

For the power allocator thermal governor, I am aware, as I am reviewing
it. I am more interested in other users of power models, a part from
thermal subsystem.

> 
> 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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