Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 25 Apr 2019 14:04:10 +0200 | Subject | Re: [PATCH V3 3/3] thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping |
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On Thu, 25 Apr 2019 at 12:45, Quentin Perret <quentin.perret@arm.com> wrote: > > 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.
They would better use the sysfs set_target interface of cpu_cooling device in this case.
> > 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.
That would be the goal, if userspace uses the sysfs interface of cpufreq to set a new max frequency, it should be considered as a long change in regards to the scheduling rate and in this case it should be interesting to update cpacity_orig and rebuild sched_domain.
> > > 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
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