linux-kernel - Re: v2.6.26-rc7: Negative powertop values

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Message-ID: <487A20DF.7060701@linux.intel.com>
Date:	Sun, 13 Jul 2008 08:35:59 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Pavel Machek <pavel@...e.cz>
CC:	Vegard Nossum <vegard.nossum@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: v2.6.26-rc7: Negative powertop values

Pavel Machek wrote:
> On Tue 2008-07-08 06:52:51, Arjan van de Ven wrote:
>> On Sun, 6 Jul 2008 21:48:45 +0200
>> Pavel Machek <pavel@...e.cz> wrote:
>>
>>>> [I assume you know that doing a software unplug you burn more power
>>>> than by leaving the cpu idle]
>>> We should really fix that one day...
>> yeah but it's incredibly hard to get right (in the light of the bios
>> constantly changing what our allowed C-states are)... and the best case
> 
> What can happen there? So BIOS decides C4 may no longer be cool idea
> because we have AC power now, but that does not mean C4 stops working,
> right?

or it decides that your voltage regulator needs to operate in a certain mode and the voltage for C4 is no longer
available. or .. or ...

> 
> How is changing allowed C-states list supposed to work, anyway? I
> mean, we may be in one of those on other CPU when BIOS decides to
> change the list...

you get an interrupt to notify you of the change ;-)

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