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 02:35:05 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dirk Brandewie <dirk.brandewie@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Morten Rasmussen <morten.rasmussen@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.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, jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC PATCH 06/16] arm: topology: Define TC2 sched energy and
 provide it to scheduler

On Tue, Jun 10, 2014 at 12:16:22PM +0200, Peter Zijlstra wrote:
> What other target would you optimize for? The purpose here is to build
> an energy aware scheduler, one that schedules tasks so that the total
> amount of energy, for the given amount of work, is minimal.
> 
> So we can't measure in Watt, since if we forced the CPU into the lowest
> P-state (or even C-state for that matter) work would simply not
> complete. So we need a complete energy term.
> 
> Now. IPC is instructions/cycle, Watt is Joule/second, so IPC/Watt is
> 
> instructions   second
> ------------ * ------ ~ instructions / joule
>   cycle        joule
> 
> Seeing how both cycles and seconds are time units.
> 
> So for any given amount of instructions, the work needs to be done, we
> want the minimal amount of energy consumed, and IPC/Watt is the natural
> metric to measure this over an entire workload.

Ok, I understand. Whether we take IPC/watt as an input metric in scheduler or
as a goal for scheduler, we definitely need to try both.

Thanks, Peter.

Yuyang
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