[Nouveau] [Discussion] User controls for PowerManagement
mjg59 at srcf.ucam.org
Tue Jan 12 12:59:27 PST 2010
The real question is what you want to be controlling. The two factors
that we can actually influence are voltage and frequency - and on some
cards we're limited to frequency. Everything else is then constrained by
that choice. So the only thing that it makes sense to expose to
userspace here is the frequency. As others have suggested, policy is
probably best described in terms of either performance (fixed maximum
frequency) or powersave (ondemand frequency shifting).
That's not to say that there aren't other constraints people may want to
impose, but they're orthogonal. A user may want to stop their GPU from
running at more than a certain temperature. That can be achieved by
leaving this interface as is, but hooking it into the kernel thermal
zone code. The user can then set a temperature limit and the kernel will
automatically slow the chip down whenever it gets near that temperature.
Since this is effectively a proxy for fan speed, that also gets catered
So I think a general policy knob (like scaling_cur_governor in cpufreq)
ought to be sufficient here, possibly along with an indication of the
instantaneous frequency because some people seem to like that kind of
thing. Anything else sounds like overengineering.
Matthew Garrett | mjg59 at srcf.ucam.org
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