linux-kernel - Re: [discussion]sched: a rough proposal to enable power saving in scheduler

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Message-ID: <5033A790.2060004@linux.intel.com>
Date:	Tue, 21 Aug 2012 08:21:52 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Matthew Garrett <mjg59@...f.ucam.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Alex Shi <alex.shi@...el.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	vincent.guittot@...aro.org, svaidy@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in
 scheduler


>>> A modern kernel better know what state the system is in: on 
>>> battery or on AC power.
>>
>> That's a fundamentally uninteresting thing for the kernel to 
>> know about. [...]
> 
> I disagree.

and I'll agree with Matthew and disagree with you ;-)

> 
>> [...] AC/battery is just not an important power management 
>> policy input when compared to various other things.
> 
> Such as?
> 
> The thing is, when I use Linux on a laptop then AC/battery is 
> *the* main policy input.

I think you're wrong there.
First of all, not the whole world is a laptop.
Phones and servers are very different than laptops in this sense.
In a phone, when you're charging, you want to be EXTRA power efficient in many ways
(since charging creates heat, and that heat will take away your thermal budget).
In a datacenter, you're either on AC or DC all the time, and power efficiency still matters.

And even on a laptop.. heat production matters even when on AC... laptops are more and more like phones
that way.

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