Re: [PATCH V3 3/3] thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping

Quentin Perret
2019-04-25T10:45:19Z

On Tuesday 23 Apr 2019 at 18:38:46 (-0400), Thara Gopinath wrote:
> I think there is one major difference between user-defined frequency
> constraints and frequency constraints due to thermal events in terms of
> the time period the system spends in the the constraint state.
> Typically, a user constraint lasts for seconds if not minutes and I
> think in this case cpu_capacity_orig should reflect this constraint and
> not cpu_capacity like this patch set.

That might not always be true I think. There's tons of userspace thermal
deamons out there, and I wouldn't be suprised if they were writing into
the cpufreq sysfs files, although I'm not sure.

Another thing is, if you want to change the capacity_orig value, you'll
need to rebuild the sched domains and all I believe. Otherwise there is
a risk to 'break' the sd_asym flags. So we need to make sure we're happy
to pay that price.

> Also, in case of the user
> constraint, there is possibly no need to accumulate and average the
> capacity constraints and instantaneous values can be directly applied to
> cpu_capacity_orig. On the other hand thermal pressure is more spiky and
> sometimes in the order of ms and us requiring the accumulating and
> averaging.
> >
> > Perhaps the Intel boost stuff could be factored in there ? That is,
> > at times when the boost freq is not reachable capacity_of() would appear
> > smaller ... Unless this wants to be reflected instantaneously ?
> Again, do you think intel boost is more applicable to be reflected in
> cpu_capacity_orig and not cpu_capacity?

I'm not even sure if we want to reflect it at all TBH, but I'd be
interested to see what Intel folks think :-)

Thanks,
Quentin