Messages in this thread | | | Date | Wed, 30 May 2018 17:57:34 +0100 | From | Patrick Bellasi <> | Subject | Re: [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional frequency invariant accounting |
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Hi Peter, maybe you missed this previous my response: 20180518133353.GO30654@e110439-lin ?
Would like to have your tought about the concept of "transient maximum capacity" I was describing...
On 18-May 14:33, Patrick Bellasi wrote: > On 18-May 13:29, Peter Zijlstra wrote: > > On Fri, May 18, 2018 at 11:57:42AM +0100, Patrick Bellasi wrote: > > > Thus, my simple (maybe dumb) questions are: > > > - why can't we just fold turbo boost frequency into the existing concepts? > > > - what are the limitations of such a "simple" approach? > > > > Perhaps... but does this not further complicate the whole capacity vs > > util thing we already have in say the misfit patches? > > Not sure about that... > > > And the util_fits_capacity() thing from the EAS ones. > > In this case instead, if we can track somehow (not saying we can) > what is the currently available "transient maximum capacity"... > then a util_fits_capacity() should just look at that. > > If the transient capacity is already folded into cpu_capacity, as it > is now for RT and IRQ pressure, then likely we don't have to change > anything. > > > The thing is, we either need to dynamically scale the util or the > > capacity or both. I think for Thermal there are patches out there that > > drop the capacity. > > Not sure... but I would feel more comfortable by something which caps > the maximum capacity. Meaning, eventually you can fill up the maximum > possible capacity only "up to" a given value, because of thermal or other > reasons most of the scheduler maybe doesn't even have to know why? > > > But we'd then have to do the same for turbo/vector and all the other > > stuff as well. Otherwise we risk things like running at low U with 0% > > idle and not triggering the tipping point between eas and regular > > balancing. > > Interacting with the tipping point and/or OPP changes is indeed an > interesting side of the problem I was not considering so far... > > But again, the tipping point could not be defined as a delta > with respect to the "transient maximum capacity" ? > > > So either way around we need to know the 'true' max, either to fudge > > util or to fudge capacity. > > Right, but what I see from a concepts standpoint is something like: > > +--+--+ cpu_capacity_orig (CONSTANT at boot time) > | | | > | | | HW generated constraints > | v | > +-----+ cpu_capacity_max (depending on thermal/turbo boost) > | | | > | | | SW generated constraints > | v | > +-----+ cpu_capacity (depending on RT/IRQ pressure) > | | | > | | | tipping point delta > +--v--+ > | | Energy Aware mode available capacity > +-----+ > > Where all the wkp/lb heuristics are updated to properly consider the > cpu_capacity_max metrics whenever it comes to know what is the max > speed we can reach now on a CPU. > > > And I'm not sure we can know in some of these cases :/ > > Right, this schema will eventually work only under the hypothesis that > "somehow" we can update cpu_capacity_max from HW events. > > Not entirely sure that's possible and/or at which time granularity on > all different platforms. > > > And while Vincent's patches might have been inspired by another problem, > > they do have the effect of always allowing util to go to 1, which is > > nice for this. > > Sure, that's a nice point, but still I have the feeling that always > reaching u=1 can defeat other interesting properties of a task, > For example, comparing task requirements in different CPUs and/or at > different times, which plays a big role for energy aware task > placement decisions. > > -- > #include <best/regards.h> > > Patrick Bellasi
-- #include <best/regards.h>
Patrick Bellasi
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