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

On 11/17/21 7:49 AM, Rafael J. Wysocki wrote:
> On Wed, Nov 17, 2021 at 11:46 AM Lukasz Luba <> 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
>>> <> 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)

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