Re: [PATCH v3 0/3] Add support for AArch64 AMUv1-based arch_freq_get_on_cpu

[Sumit Gupta]

Hi Beata,

> > On Tuesday 12 Mar 2024 at 08:34:28 (+0000), Beata Michalska wrote:
> > > Introducing arm64 specific version of arch_freq_get_on_cpu, cashing on
> > > existing implementation for FIE and AMUv1 support: the frequency scale
> > > factor, updated on each sched tick, serves as a base for retrieving
> > > the frequency for a given CPU, representing an average frequency
> > > reported between the ticks - thus its accuracy is limited.
> > >
> > > The changes have been rather lightly (due to some limitations) tested on
> > > an FVP model.
> > >
> > > Relevant discussions:
> > > [1] https://lore.kernel.org/all/20240229162520.970986-1-vanshikonda@xxxxxxxxxxxxxxxxxxxxxx/
> > > [2] https://lore.kernel.org/all/7eozim2xnepacnnkzxlbx34hib4otycnbn4dqymfziqou5lw5u@5xzpv3t7sxo3/
> > > [3] https://lore.kernel.org/all/20231212072617.14756-1-lihuisong@xxxxxxxxxx/
> > > [4] https://lore.kernel.org/lkml/ZIHpd6unkOtYVEqP@xxxxxxxxxxxxxxxxxxxxxxxxx/T/#m4e74cb5a0aaa353c60fedc6cfb95ab7a6e381e3c
> > >
> > > v3:
> > > - dropping changes to cpufreq_verify_current_freq
> > > - pulling in changes from Ionela initializing capacity_freq_ref to 0
> > >    (thanks for that!)  and applying suggestions made by her during last review:
> > >      - switching to arch_scale_freq_capacity and arch_scale_freq_ref when
> > >        reversing freq scale factor computation
> > >      - swapping shift with multiplication
> > > - adding time limit for considering last scale update as valid
> > > - updating frequency scale factor upon entering idle
> > >
> > > v2:
> > > - Splitting the patches
> > > - Adding comment for full dyntick mode
> > > - Plugging arch_freq_get_on_cpu into cpufreq_verify_current_freq instead
> > >    of in show_cpuinfo_cur_freq to allow the framework to stay more in sync
> > >    with potential freq changes
> > >
> > > Beata Michalska (2):
> > >    arm64: Provide an AMU-based version of arch_freq_get_on_cpu
> > >    arm64: Update AMU-based frequency scale factor on entering idle
> > >
> > > Ionela Voinescu (1):
> > >    arch_topology: init capacity_freq_ref to 0
> >
> > Should there have been a patch that adds a call to
> > arch_freq_get_on_cpu() from show_cpuinfo_cur_freq() as well?
> >
> > My understanding from this [1] thread and others referenced there is
> > that was something we wanted.
> Right, so I must have missunderstood that, as the way I did read it was that
> it is acceptable to keep things as they are wrt cpufreq sysfs entries.
>
> ---
> BR
> Beata
> > [1] https://lore.kernel.org/lkml/2cfbc633-1e94-d741-2337-e1b0cf48b81b@xxxxxxxxxx/
> >
> > Thanks,
> > Ionela.

Yes, the change to show_cpuinfo_cur_freq from [1] is needed.

[1] 
https://lore.kernel.org/lkml/20230606155754.245998-1-beata.michalska@xxxxxxx/

Thank you,
Sumit Gupta