Re: [PATCH v10 2/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Sudeep Holla <sudeep.holla@arm.com>]

On Mon, Feb 17, 2025 at 03:07:24PM +0000, Ionela Voinescu wrote:
> Hi Catalin,
> 
> On Monday 17 Feb 2025 at 14:57:53 (+0000), Catalin Marinas wrote:
> > On Mon, Feb 17, 2025 at 12:52:44PM +0100, Rafael J. Wysocki wrote:
> > > On Fri, Jan 31, 2025 at 5:25 PM Beata Michalska <beata.michalska@arm.com> wrote:
> > > >
> > > > Currently the CPUFreq core exposes two sysfs attributes that can be used
> > > > to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
> > > > and scaling_cur_freq. Both provide slightly different view on the
> > > > subject and they do come with their own drawbacks.
> > > >
> > > > cpuinfo_cur_freq provides higher precision though at a cost of being
> > > > rather expensive. Moreover, the information retrieved via this attribute
> > > > is somewhat short lived as frequency can change at any point of time
> > > > making it difficult to reason from.
> > > >
> > > > scaling_cur_freq, on the other hand, tends to be less accurate but then
> > > > the actual level of precision (and source of information) varies between
> > > > architectures making it a bit ambiguous.
> > > >
> > > > The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
> > > > distinct interface, exposing an average frequency of a given CPU(s), as
> > > > reported by the hardware, over a time frame spanning no more than a few
> > > > milliseconds. As it requires appropriate hardware support, this
> > > > interface is optional.
> > > >
> > > > Note that under the hood, the new attribute relies on the information
> > > > provided by arch_freq_get_on_cpu, which, up to this point, has been
> > > > feeding data for scaling_cur_freq attribute, being the source of
> > > > ambiguity when it comes to interpretation. This has been amended by
> > > > restoring the intended behavior for scaling_cur_freq, with a new
> > > > dedicated config option to maintain status quo for those, who may need
> > > > it.
> > > 
> > > In case anyone is waiting for my input here
> > > 
> > > Acked-by: Rafael J. Wysocki <rafael@kernel.org>
> > > 
> > > for this and the previous patch and please feel free to route them
> > > both through ARM64.
> > 
> > Thanks Rafael. I indeed plan to take them through the arm64 tree.
> 
> Just a mention that this set depends on the patch that Beata linked at
> [6]. That patch applies cleanly on next-20250217 and it still
> builds/boots/works as expected.
> 

Ah I see it is indeed dependent. Just responded on the other thread before
reading this. So it is better if Catalin picks up [6] as well. Sorry for
the confusion.

-- 
Regards,
Sudeep

[6] https://lore.kernel.org/all/20240827154818.1195849-1-ionela.voinescu@arm.com/