linux-kernel - Re: [PATCH] arm64: Provide an AMU-based version of arch_freq_get_on

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Message-ID: <20230727095604.GA18721@willie-the-truck>
Date:   Thu, 27 Jul 2023 10:56:05 +0100
From:   Will Deacon <will@...nel.org>
To:     Beata Michalska <beata.michalska@....com>
Cc:     Sudeep Holla <sudeep.holla@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, mark.rutland@....com, rafael@...nel.org,
        viresh.kumar@...aro.org, ionela.voinescu@....com,
        sumitg@...dia.com, yang@...amperecomputing.com
Subject: Re: [PATCH] arm64: Provide an AMU-based version of
 arch_freq_get_on_cpu

On Wed, Jun 07, 2023 at 03:00:49PM +0100, Beata Michalska wrote:
> On Wed, Jun 07, 2023 at 10:58:56AM +0100, Sudeep Holla wrote:
> > On Tue, Jun 06, 2023 at 04:57:54PM +0100, Beata Michalska wrote:
> > > With the Frequency Invariance Engine (FIE) being already wired up with
> > > sched tick and making use of relevant (core counter and constant
> > > counter) AMU counters, getting the current frequency for a given CPU
> > > on supported platforms, can be achieved by utilizing the frequency scale
> > > factor which reflects an average CPU frequency for the last tick period
> > > length.
> > > 
> > > With that at hand, arch_freq_get_on_cpu dedicated implementation
> > > gets enrolled into cpuinfo_cur_freq policy sysfs attribute handler,
> > > which is expected to represent the current frequency of a given CPU,
> > > as obtained by the hardware. This is exactly the type of feedback that
> > > cycle counters provide.
> > > 
> > > In order to avoid calling arch_freq_get_on_cpu from the scaling_cur_freq
> > > attribute handler for platforms that do provide cpuinfo_cur_freq, and
> > > yet keeping things intact for those platform that do not, its use gets
> > > conditioned on the presence of cpufreq_driver (*get) callback (which also
> > > seems to be the case for creating cpuinfo_cur_freq attribute).
> > >
> > 
> > LGTM,
> > 
> > Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> > 
> Thanks for the review.
> > However I fail to understand if both the changes are dependent ?
> > Can this be split into 2 patches ? I fail to see the dependency, what
> > am I missing ? Even if there is some dependency to get arch value
> > (arch_freq_get_on_cpu() from show_cpuinfo_cur_freq()), you can push
> > that change first followed by the arm64 change as 2 different change.
> > 
> I guess I could split the patch into two parts:
> 1. adding implementation for the arch_freq_get_on_cpu
> 2. wiring it up with the cpufreq relevant attrib handlers
> 
> or the other way round (if that's what you have in mind).
> 
> Will wait a bit for any further comments before pushing new v.

Are you still planning on a v2?

Will