Date: Thu, 18 Nov 2004 10:52:51 +0100 From: Bruno Ducrot <ducrot@poupinou.org> To: Nate Lawson <nate@root.org> Cc: acpi@FreeBSD.org Subject: Re: Why C3 state isn't entered? Message-ID: <20041118095251.GZ31422@poupinou.org> In-Reply-To: <419BC119.4040209@root.org> References: <419BB14C.1060301@delit.net> <419BB438.3040906@root.org> <419BBFAA.3000605@delit.net> <419BC119.4040209@root.org>
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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.
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