Date: Thu, 6 May 2004 08:50:33 -0700 (PDT) From: Nate Lawson <nate@root.org> To: Mike Silbersack <silby@silby.com> Cc: acpi@freebsd.org Subject: Re: power savings and usb Message-ID: <20040506084132.L41848@root.org> In-Reply-To: <20040506035840.G811@odysseus.silby.com> References: <200405052004.i45K4EnF029671@repoman.freebsd.org> <20040505171634.N37631@root.org> <20040506025051.V630@odysseus.silby.com> <20040506034307.M811@odysseus.silby.com> <20040506035840.G811@odysseus.silby.com>
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[moved to acpi@] On Thu, 6 May 2004, Mike Silbersack wrote: > On Thu, 6 May 2004, Mike Silbersack wrote: > > > Good deal, it works as avertised. I even learned a bit of shell scripting > > in the process of writing a simple speed switching script. :) > > > > Of course, the real question is whether or not it'll actually help battery > > life at all; this is a mobile celeron, I suspect that I won't have much of > > an impact. Ah well. Using the C3 idle state makes my laptop noticeably cooler and the fan doesn't come on in normal usage. > Gah, except that my experiment in clockswitching made the usb stack mad, > so it's constantly priniting "usb0: X scheduling overruns", where X > appears to be a number containing one or two bits of entropy per second. > I will have to go visit ohci.c with a cluebat when I get a chance. > > Er, it stopped when I plugged in the power cord, and starts again when I > unplugged it. Is it possible that ohci.c is reading some USB voltage > value instead of the overrun bit that it thinks it is reading? Nope, we auto-switch cpu idle values (and optionally throttle states) on AC line transition. See /etc/rc.d/power_profile and the options in /etc/defaults/rc.conf: performance_cx_lowest="HIGH" # Online CPU idle state performance_throttle_state="HIGH" # Online throttling state economy_cx_lowest="LOW" # Offline CPU idle state economy_throttle_state="HIGH" # Offline throttling state The default online is to use C1 (or HLT as it's known elsewhere). This is existing behavior. The default offline is to switch to the lowest state available. On my laptop, this is C3. (The default for throttling is to leave it off since it is more disruptive). The problem with C3 is that if you have USB loaded, it is rarely used for idling as USB constantly uses bus mastering in polling for new devices. This is ok since we demote to C2 in this case. You can observe this via sysctl hw.acpi.cpu: hw.acpi.cpu.cx_supported: C1/0 C2/84 C3/120 hw.acpi.cpu.cx_lowest: 1 hw.acpi.cpu.cx_history: 9175/0 173443/9175 0/0 This means I am requesting a lowest sleep of C2 (idx 1 of the options supported). The history values show that I haven't used C3 at all and am using C2 at a rate of about 95%. ohci may have problems with C3. On my uhci, it demotes to C2 without causing problems. You can override this by setting in /etc/rc.conf: economy_cx_lowest="1" -Nate
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