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

Rafael J. Wysocki
2016-03-04T01:14:11Z

On Thu, Mar 3, 2016 at 5:47 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Mar 03, 2016 at 05:37:35PM +0100, Peter Zijlstra wrote:
>> On Thu, Mar 03, 2016 at 05:24:32PM +0100, Rafael J. Wysocki wrote:
>> > >> f = a * x + b
>
>> > If not, then I think it's reasonable to map the middle of the
>> > available frequency range to x = 0.5 and then we have b = 0 and a =
>> > (max_freq + min_freq) / 2.

That actually should be a = max_freq + min_freq, because I want
(max_freq + min_freq) / 2 = a / 2.

>> So I really think that approach falls apart on the low util bits, you
>> effectively always run above min speed, even if min is already vstly
>> over provisioned.
>
> Ah nevermind, I cannot read. Yes that is worth trying I suppose. But the
> b=0,a=1 thing seems more natural still.

It is somewhat imbalanced, though. If all of the values of x are
equally probable (or equally frequent), the probability of running
above the middle frequency is lower than the probability of running
below it.