Date: Sun, 10 Oct 2010 20:49:30 +0000 From: "b. f." <bf1783@googlemail.com> To: Bruce Cran <bruce@cran.org.uk> Cc: freebsd-questions@FreeBSD.org Subject: Re: VIA EPIA 5000 and ACPI Cx levels Message-ID: <AANLkTimnavr=uZhwSgRnBtNFPuPbQq6Ta4Tvhi8MQ1aS@mail.gmail.com>
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>I recently upgraded to HEAD on my VIA EPIA C3 box, and had thought about >trying out the new one-shot timer mode. Reading mav@'s email it seems that >since it doesn't have LAPIC or HPET timers it won't work. However I thought I >should still get power savings by using higher Cx levels, but setting >hw.acpi.cpu.cx_lowest to C3 I'm only seeing 0.8% time spent in C2 mode, the >rest being in C1. The CPU's idle so I don't understand why it's not going into >deeper sleep modes. Is this likely to just be an ACPI bug? If it has an i8254, that can also be used in one-shot mode if hint.attimer.0.timecounter=0 is used, since r212778. But for low values of kern.hz, I've found that periodic mode can result in fewer interrupts (albeit increased latencies and lower accuracy in accounting) than one-shot mode, if kern.eventtimer.singlemul=1. As for the power-saving states, are you using a simple 'sysctl dev.cpu.0.cx_usage' to find the percentages? If you're doing something more involved, you may be affecting the measurements. Also, does the system think that the deeper sleep states are available on your machine? If so, what are their latencies? If they are high, they may be used less often, or not at all. Did you follow some of the other recommendations to allow more sleeping, like at: http://wiki.freebsd.org/TuningPowerConsumption ? Or apply mav's extra patch to further reduce interrupts: http://people.freebsd.org/~mav/tm6292_idle.patch ? b.
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