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Date: Thu, 18 Nov 2004 10:52:51 +0100
To: Nate Lawson <nate@root.org>
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From: Bruno Ducrot <ducrot@poupinou.org>
cc: acpi@FreeBSD.org
Subject: Re: Why C3 state isn't entered?
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On Wed, Nov 17, 2004 at 01:22:33PM -0800, Nate Lawson wrote:
> If you have the USB driver (usb.ko) loaded or compiled into the kernel, 
> you can't use C3.  The way to disable it is to implement support for 
> idling ports in uhci, ehci, and ohci.  C3 doesn't make a huge difference 
> (2-5%?) compared to C2 although it does help.  I did some profiling of 
> this a while back and found that the top three power saving features are 
> dimming the display (by far the most), changing CPU frequency (similar 
> but definitely less), and C2/C3 (better than C1 but not nearly as much 
> savings as the first two).
> 

Spin down disks is maybe more important than CPU frequency scaling also.

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.