Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler utilization data

Peter Zijlstra
2016-03-10T08:43:49Z

On Thu, Mar 10, 2016 at 12:28:52AM +0100, Rafael J. Wysocki wrote:
> > [ I would not have chosen (1 + 1/n), but lets stick to that ]
>
> Well, what would you choose then? :-)

1/p ; 0 < p < 1

or so. Where p then represents the percentile threshold where you want
to bump to the next freq.

> I think that should be
>
> next_freq = (1 + 1/n) * max_freq * util / max
>
> (where max is the second argument of cpufreq_update_util) or the
> dimensions on both sides don't match.

Well yes, but so far we were treating util (and util_raw) as 0 < u < 1,
values, so already normalized against max.

But yes..

> > if we substitute (2) into (3) we get:
> >
> > = (1 + 1/n) * max_freq * util_raw * current_freq / max_freq
> > = (1 + 1/n) * current_freq * util_raw (4)
> >
> > Which gets you two formula with the same general behaviour. As (2) is
> > the only approximation of (1) we can make.
>
> OK
>
> So since utilization is not frequency invariant in the current
> mainline (or linux-next for that matter) AFAIC, I'm going to use the
> following in the next version of the schedutil patch series:
>
> next_freq = 1.25 * current_freq * util_raw / max
>
> where util_raw and max are what I get from cpufreq_update_util().
>
> 1.25 is for the 80% tipping point which I think is reasonable.

OK.