Hi Yicong, On Wednesday 09 Mar 2022 at 18:21:30 (+0800), Yicong Yang wrote: > Hi Ionela, > > On 2022/3/3 2:09, Ionela Voinescu wrote: > > Define topology_init_cpu_capacity_cppc() to use highest performance > > values from _CPC objects to obtain and set maximum capacity information > > for each CPU. acpi_cppc_processor_probe() is a good point at which to > > trigger the initialization of CPU (u-arch) capacity values, as at this > > point the highest performance values can be obtained from each CPU's > > _CPC objects. Architectures can therefore use this functionality > > through arch_init_invariance_cppc(). > > > > The performance scale used by CPPC is a unified scale for all CPUs in > > the system. Therefore, by obtaining the raw highest performance values > > from the _CPC objects, and normalizing them on the [0, 1024] capacity > > scale, used by the task scheduler, we obtain the CPU capacity of each > > CPU. > > > > So we're going to use highest performance rather than nominal performance, > and I checked the discussion in v2 [1]. Maybe we should also document this > in sched-capacity.rst that where scheduler get the capacity from on ACPI > based system? Currently we only have DT part but after this patch it's > also supported on ACPI based system. > It's a very good point. I'll send a separate patch for this with added information in "3.1 CPU capacity" in sched-capacity.rst. I'll send this separate and not with the rebase that Rafael requested to avoid confusing things. > Out of curiosity, since we have raw capacity now on ACPI system, seems we > are able to scale the capacity with freq_factor now? looked into > register_cpufreq_notifier(). > The freq_factor is only used for DT systems where one provides "capacity-dmips-mhz" in DT. This entry actually represents DMIPS/MHz. So the freq_factor, set to: per_cpu(freq_factor, cpu) = policy->cpuinfo.max_freq / 1000; is used to obtain the performance at the maximum frequency, basically DMIPS = (Dhrystone) million instructions per second, by multiplying this raw value from DT with the freq_factor. After this, all these value for each CPU type are normalized on a scale [0, 1024], resulting in what we call CPU capacity. For ACPI systems freq_factor will have the default value of 1 when we call topology_normalize_cpu_scale(), as the performance value obtained from _CPC is already representative for the highest frequency of the CPU and not performance/Hz as we get from DT. Therefore, we are not and should not use a freq_factor here. Hopefully I understood your question correctly. Thanks, Ionela. > [1] https://lore.kernel.org/lkml/Yh5OAsYVBWWko+CH@xxxxxxx/ > > Thanks, > Yicong
