Messages in this thread | | | Date | Mon, 21 Nov 2016 13:26:22 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits |
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On Mon, Nov 21, 2016 at 12:14:32PM +0000, Juri Lelli wrote: > On 21/11/16 11:19, Peter Zijlstra wrote:
> > So no tunables and rate limits here at all please. > > > > During LPC we discussed the rampup and decay issues and decided that we > > should very much first address them by playing with the PELT stuff. > > Morton was going to play with capping the decay on the util signal. This > > should greatly improve the ramp-up scenario and cure some other wobbles. > > > > The decay can be set by changing the over-all pelt decay, if so desired. > > > > Do you mean we might want to change the decay (make it different from > ramp-up) once for all, or maybe we make it tunable so that we can > address different power/perf requirements?
So the limited decay would be the dominant factor in ramp-up time, leaving the regular PELT period the dominant factor for ramp-down.
(Note that the decay limit would only be applied on the per-task signal, not the accumulated signal.)
It could be an option, for some, to build the kernel with a PELT window of 16ms or so (half its current size), this of course means regenerating all the constants etc.. And this very much is a compile time thing.
We could fairly easy; if this is so desired; make the PELT window size a CONFIG option (hidden by default).
But like everything; patches should come with numbers justifying them etc..
> > Also, there was the idea of; once the above ideas have all been > > explored; tying the freq ram rate to the power curve. > > > > Yep. That's an interesting one to look at, but it might require some > time.
Sure, just saying that we should resist knobs until all other avenues have been explored. Never start with a knob.
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