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

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Message-ID: <Zg3KeYoIozB01fJp@arm.com>
Date: Wed, 3 Apr 2024 23:30:33 +0200
From: Beata Michalska <beata.michalska@....com>
To: Sumit Gupta <sumitg@...dia.com>
Cc: Ionela Voinescu <ionela.voinescu@....com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	vanshikonda@...amperecomputing.com, sudeep.holla@....com,
	will@...nel.org, catalin.marinas@....com,
	vincent.guittot@...aro.org, yang@...amperecomputing.com,
	lihuisong@...wei.com, linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 0/3] Add support for AArch64 AMUv1-based
 arch_freq_get_on_cpu

On Wed, Mar 20, 2024 at 10:22:22PM +0530, Sumit Gupta wrote:
> 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@os.amperecomputing.com/
> > > > [2] https://lore.kernel.org/all/7eozim2xnepacnnkzxlbx34hib4otycnbn4dqymfziqou5lw5u@5xzpv3t7sxo3/
> > > > [3] https://lore.kernel.org/all/20231212072617.14756-1-lihuisong@huawei.com/
> > > > [4] https://lore.kernel.org/lkml/ZIHpd6unkOtYVEqP@e120325.cambridge.arm.com/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@nvidia.com/
> > > 
> > > Thanks,
> > > Ionela.
> > > 
> 
> Yes, the change to show_cpuinfo_cur_freq from [1] is needed.
>
Noted. Will send an update including fixes and this requested change.

---
BR
Beata
> [1]
> https://lore.kernel.org/lkml/20230606155754.245998-1-beata.michalska@arm.com/
> 
> Thank you,
> Sumit Gupta