Re: cpufreq: intel_pstate: map utilization into the pstate range

[Rafael J. Wysocki]

On Sun, Dec 19, 2021 at 11:10 PM Francisco Jerez <currojerez@xxxxxxxxxx> wrote:
>
> Julia Lawall <julia.lawall@xxxxxxxx> writes:
>
> > On Sat, 18 Dec 2021, Francisco Jerez wrote:

[cut]

> > I did some experiements with forcing different frequencies.  I haven't
> > finished processing the results, but I notice that as the frequency goes
> > up, the utilization (specifically the value of
> > map_util_perf(sg_cpu->util) at the point of the call to
> > cpufreq_driver_adjust_perf in sugov_update_single_perf) goes up as well.
> > Is this expected?
> >
>
> Actually, it *is* expected based on our previous hypothesis that these
> workloads are largely latency-bound: In cases where a given burst of CPU
> work is not parallelizable with any other tasks the thread needs to
> complete subsequently, its overall runtime will decrease monotonically
> with increasing frequency, therefore the number of instructions executed
> per unit of time will increase monotonically with increasing frequency,
> and with it its frequency-invariant utilization.

But shouldn't these two effects cancel each other if the
frequency-invariance mechanism works well?