Date: Thu, 18 Nov 2004 09:44:10 -0800 From: Nate Lawson <nate@root.org> To: Bruno Ducrot <ducrot@poupinou.org> Cc: acpi@FreeBSD.org Subject: Re: Why C3 state isn't entered? Message-ID: <419CDF6A.9090507@root.org> In-Reply-To: <20041118095251.GZ31422@poupinou.org> References: <419BB14C.1060301@delit.net> <419BB438.3040906@root.org> <419BBFAA.3000605@delit.net> <419BC119.4040209@root.org> <20041118095251.GZ31422@poupinou.org>
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Bruno Ducrot wrote: > 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. At least on my laptop, that didn't make much difference. But we have old behavior for many things like the syncer that is not power-aware so spinning down disks may not be as helpful. BTW, interested in implementing S4-OS for FreeBSD? :) -Nate
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