Power consumption tuning
smithi at nimnet.asn.au
Wed Aug 10 16:55:10 UTC 2016
In freebsd-questions Digest, Vol 636, Issue 4, Message: 2
On Tue, 9 Aug 2016 17:23:45 +0300 Aleksander Alekseev <afiskon at devzen.ru> wrote:
> I'm exploring how power consumption could be tuned on FreeBSD 11.0. I
> discovered a few useful articles, for instance . Also useful pieces
> of advice were given on IRC. Resulting list is for now like this:
> * Use lightweight software (i3, GTK based GUI applications, etc), turn
> off unused kernel modules, don't use full disc encryption, etc
You don't need to 'turn off' unused modules, just don't load what you
don't need :) More a memory use than power consumption issue?
> * Reduce CPU frequency (sysctl dev.cpu.0.freq), use powerd to do it
Yes. Its default parameters are usually a useful starting point.
> * Reduce display brightness (sudo pkg install intel-backlight)
> * Enable power save mode on NIC (sudo ifconfig wlan0 powersave)
Check that your particular NIC works well in powersave mode.
> * Disable unused USB devices (sudo usbconfig -d X.Y power_off)
This might not win much, at least my webcam device saved maybe 150mW,
and it wasn't good through suspend / resume without some fiddling.
> * Reduce clock frequency (kern.hz = 100)
I'm not convinced this wins much, power-wise, any more. With modern
event counters mechanism - here HPET, one-shot mode - and kern.hz=1000 I
see no more than 65-75 clock interrupts/s when idle, 2-300/s busy ..
and that's on FreeBSD 9.3.
> * Make sure your kernel is built without INVARIANTS and WITNESS
You haven't said if this is for a desktop or laptop machine, two very
different power consumption scenarios. Mention of  would suggest a
laptop as that's what mav@'s work was focussed on there.
> Perhaps there are other methods I didn't notice? For instance are there
> any other sysctl parameters or kernel configuration options worth
Well  stresses the importance of using maximum available C-states on
your hardware. But except for powerd and C-states where possible, I
wouldn't bother with all that to save an extra few watts on a desktop.
>  https://wiki.freebsd.org/TuningPowerConsumption
> Best regards,
> Aleksander Alekseev
What hardware? What OS version?
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