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

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Message-ID: <20080714062644.GE31949@elf.ucw.cz>
Date:	Mon, 14 Jul 2008 08:26:44 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Arjan van de Ven <arjan@...ux.intel.com>
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

On Sun 2008-07-13 08:35:59, Arjan van de Ven wrote:
> 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 ;-)

But that's too late, right? You may be actively using that Cstate on
another CPU...
									Pavel

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