Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits

From: Peter Zijlstra
Date: Mon Nov 21 2016 - 09:43:55 EST

On Mon, Nov 21, 2016 at 02:37:27PM +0000, Juri Lelli wrote:
> On 21/11/16 15:17, Peter Zijlstra wrote:

> > Not sure I follow. So by limiting decay to the task value, the moment we
> > add it back to the accumulated signal (wakeup), the accumulated signal
> > jumps up quickly and ramp-up is achieved.
> >
> This is true, but it seems that this potentially spiky behaviour
> (which in general depends on tasks composition and periodicity) might
> affect power savings (as in you don't generally want to switch between
> high and low freqs too often). So that's why I was just thinking that
> some sort of smoothing applied to the signal schedutil uses might help.

Hurm.. so during LPC it was said that fast ramp-up was desired. Note
that we'll not ramp down this fast, the accumulated signal will decay
slowly as per blocked-load PELT rules. So only ramp-up is spiky, but
that is what was desired AFAIU.