linux-kernel - Re: [linux-pm] Power Management framework proposal

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Date:	Mon, 23 Jul 2007 10:33:24 -0700 (PDT)
From:	david@...g.hm
To:	Ondrej Zajicek <santiago@...reenet.org>
cc:	Arjan van de Ven <arjan@...radead.org>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] Power Management framework proposal

On Mon, 23 Jul 2007, Ondrej Zajicek wrote:

> On Sun, Jul 22, 2007 at 09:19:17PM -0700, Arjan van de Ven wrote:
>> let me give you a real world example then, and the numbers I'm using are
>> ballpark the same as you'll find in a (mobile) core 2 duo datasheet, I
>> just rounded them a little so that the math works out nice.
>>
>> power at full speed: 34W
>> power at half speed: 24W
>> power at idle: 1W
>
> I have usually seen different numbers, for example:
>
> http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/30430.pdf
>
> Although this paper speaks about thermal design power instead of power
> consumption, i suppose that it should be roughly equal.
>
> For example Athlon 64 3700 (ADA3700AEP5AR):
>
> 2.4 GHz, 1.5 V -> 89 W
> 2.2 GHz, 1.4 V -> 72 W
> 2.0 GHz, 1.3 V -> 53 W
> 1.8 GHz, 1.2 V -> 39 W
> 1.0 GHz, 1.1 V -> 22 W
>
>
> Even my measurement on PC (Athlon X2, VIA K8T890) of complete PC power
> consumption shows that it is more efficient to be busy for 2 time units
> on 1 GHz than be busy for 1 time unit and be idle for 1 time unit
> on 2 GHz.
>
> 1 GHz:
> both cores idle:	48 W
> one core busy:		57 W
> two cores busy:		66 W
>
> 2 GHz:
> both cores idle:	54 W
> one core busy:		78 W
> two cores busy:		95 W

what Arjan is saying is one time unit at 2GHz with both cores busy, one 
time unit at 1GHz with both cores idle (this would be 132w/two time units 
vs 143W/two time units) still a win for running a 1GHz, but a smaller one

or better still, one time unit at 2GHz with both cores busy, one time unit 
in sleep mode, in this case if the sleep mode is any good at all it wins.

David Lang
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