linux-kernel - Re: [PATCH v2 2/2] cpufreq: CPPC: Dont read counters for idle CPUs

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Message-ID: <CAFivqmLoDv_pWdmBG8ws-CMUBXcb9bS1TgMaxW9YZMqqHpRSyA@mail.gmail.com>
Date: Mon, 21 Jul 2025 12:40:15 -0700
From: Prashant Malani <pmalani@...gle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Beata Michalska <beata.michalska@....com>, Jie Zhan <zhanjie9@...ilicon.com>, 
	Ionela Voinescu <ionela.voinescu@....com>, Ben Segall <bsegall@...gle.com>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Ingo Molnar <mingo@...hat.com>, 
	Juri Lelli <juri.lelli@...hat.com>, open list <linux-kernel@...r.kernel.org>, 
	"open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>, Mel Gorman <mgorman@...e.de>, 
	Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Valentin Schneider <vschneid@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Viresh Kumar <viresh.kumar@...aro.org>, z00813676 <zhenglifeng1@...wei.com>, sudeep.holla@....com
Subject: Re: [PATCH v2 2/2] cpufreq: CPPC: Dont read counters for idle CPUs

Hi Rafael,

Thanks for looking into this.

On Mon, 21 Jul 2025 at 10:00, Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Tue, Jul 15, 2025 at 8:28 AM Prashant Malani <pmalani@...gle.com> wrote:
> >
> > +Sudeep.
> >
> > On Mon, 14 Jul 2025 at 02:31, Beata Michalska <beata.michalska@....com> wrote:
> > > So I believe this should be handled in CPUFreq core, if at all.
> > > Would be good to get an input/opinion from the maintainers: Viresh and Rafael.
> >
> > Viresh, Rafael, Sudeep, could you kindly chime in? The unreliability
> > of this frequency
> > measurement method in CPPC is affecting the cached frequency saved by CPUFreq,
> > which in turn affects future frequency set calls.
>
> I gather that "the cached frequency saved by CPUFreq" means policy->cur.

Yes, that's right.


>
> > It would be great if we could solve this in CPUFreq core (maybe not
> > rely on the cached frequency while setting the new one [3]?)
>
> I see what you mean now.
>
> Why don't you flag the driver as CPUFREQ_NEED_UPDATE_LIMITS?
>
> That would kind of make sense given how the driver works overall, or
> am I missing anything?

Sounds fine to me (it doesn't fix the lingering accuracy issue, but at
least frequency
setting will get unblocked). I can put together a patch if there are
no objections.

Thanks,