Date: Fri, 19 Nov 2004 15:16:23 +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: <20041119141623.GF31422@poupinou.org> In-Reply-To: <419CDF6A.9090507@root.org> References: <419BB14C.1060301@delit.net> <419BB438.3040906@root.org> <419BBFAA.3000605@delit.net> <419BC119.4040209@root.org> <20041118095251.GZ31422@poupinou.org> <419CDF6A.9090507@root.org>
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On Thu, Nov 18, 2004 at 09:44:10AM -0800, Nate Lawson wrote: > 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. Well, it was more a general note. Under FreeBSD, I guess you can save something like 6 or 7% of battery remaining times if a more power aware developpement is done for DD. I don't expect much more. Under Linux, there is a need to do much more tweaks to achive a 20-30% remaining time (via the laptop-mode) due to agressive disk access in general. > BTW, interested in implementing S4-OS for FreeBSD? :) I can't promise anything yet. Cheers, -- Bruno Ducrot -- Which is worse: ignorance or apathy? -- Don't know. Don't care.
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