Re: [PATCH] base: arch_topology: Use policy->max to calculate freq_factor

[Thara Gopinath]

Hi,

On 11/17/21 7:49 AM, Rafael J. Wysocki wrote:
> On Wed, Nov 17, 2021 at 11:46 AM Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> > Hi Rafael,
> >
> > On 11/16/21 7:05 PM, Rafael J. Wysocki wrote:
> > > On Mon, Nov 15, 2021 at 9:10 PM Thara Gopinath
> > > <thara.gopinath@xxxxxxxxxx> wrote:
> > > > cpuinfo.max_freq can reflect boost frequency if enabled during boot.  Since
> > > > we don't consider boost frequencies while calculating cpu capacities, use
> > > > policy->max to populate the freq_factor during boot up.
> > >
> > > I'm not sure about this.  schedutil uses cpuinfo.max_freq as the max frequency.
> >
> > Agree it's tricky how we treat the boost frequencies and also combine
> > them with thermal pressure.
> > We probably would have consider these design bits:
> > 1. Should thermal pressure include boost frequency?
>
> Well, I guess so.
>
> Running at a boost frequency certainly increases thermal pressure.
>
> > 2. Should max capacity 1024 be a boost frequency so scheduler
> >      would see it explicitly?
>
> That's what it is now if cpuinfo.max_freq is a boost frequency.
>
> > - if no, then schedutil could still request boost freq thanks to
> >     map_util_perf() where we add 25% to the util and then
> >     map_util_freq() would return a boost freq when util was > 1024
> >
> >
> > I can see in schedutil only one place when cpuinfo.max_freq is used:
> > get_next_freq(). If the value stored in there is a boost,
> > then don't we get a higher freq value for the same util?
>
> Yes. we do, which basically is my point.
>
> The schedutil's response is proportional to cpuinfo.max_freq and that
> needs to be taken into account for the results to be consistent.

So IIUC, cpuinfo.max_freq is always supposed to be the highest supported 
frequency of a cpu, irrespective of whether boost is enabled or not. 
Where as policy->max is the currently available maximum cpu frequency 
which can be equal to cpuinfo.max_freq or lower (depending on whether 
boost is enabled, whether there is a constraint on policy->max placed by 
thermal etc). So in this case isn't it better for schedutil to consider 
policy->max instead of cpuinfo.max ? Like you mentioned above same 
utilization will relate to different frequencies depending on the 
maximum frequency.



>

--
Warm Regards
Thara (She/Her/Hers)