linux-kernel - Re: [PATCH v1] cpufreq: Add policy

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Message-ID: <5pv5tqf24p6ttpydpdegyhyod3m2hmpwbfrzl6otsq3q2gvb2s@gsgcgbcvin3u>
Date: Fri, 14 Nov 2025 10:41:03 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Samuel Wu <wusamuel@...gle.com>, peterz@...radead.org, 
	vincent.guittot@...aro.org
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, kernel-team@...roid.com, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v1] cpufreq: Add policy_frequency trace event

On 13-11-25, 19:41, Samuel Wu wrote:
> On Wed, Nov 12, 2025 at 10:45 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > On 12-11-25, 15:51, Samuel Wu wrote:
> > > The existing cpu_frequency trace_event can be verbose, emitting an event
> > > for every CPU in the policy even when their frequencies are identical.
> > >
> > > This patch adds a new policy_frequency trace event, which provides a
> > > more efficient alternative to cpu_frequency trace event. This option
> > > allows users who only need frequency at a policy level more concise logs
> > > with simpler analysis.
> > >
> > > Signed-off-by: Samuel Wu <wusamuel@...gle.com>
> > > ---
> > >  drivers/cpufreq/cpufreq.c    |  2 ++
> > >  include/trace/events/power.h | 21 +++++++++++++++++++++
> > >  2 files changed, 23 insertions(+)
> > >
> > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > > index 4472bb1ec83c..b65534a4fd9a 100644
> > > --- a/drivers/cpufreq/cpufreq.c
> > > +++ b/drivers/cpufreq/cpufreq.c
> > > @@ -345,6 +345,7 @@ static void cpufreq_notify_transition(struct cpufreq_policy *policy,
> > >               pr_debug("FREQ: %u - CPUs: %*pbl\n", freqs->new,
> > >                        cpumask_pr_args(policy->cpus));
> > >
> > > +             trace_policy_frequency(freqs->new, policy->cpu);
> > >               for_each_cpu(cpu, policy->cpus)
> > >                       trace_cpu_frequency(freqs->new, cpu);
> >
> > I don't see much value in almost duplicate trace events. If we feel that a
> > per-policy event is a better fit (which makes sens), then we can just drop the
> > trace_cpu_frequency() events and print policy->cpus (or related_cpus)
> > information along with the per-policy events.
> 
> Thank you for the feedback Viresh. Fair enough, I've done some testing
> and a single trace event should work and would be cleaner. Please let
> me know what you think of this proposal for v2.
> 
> We can append a bitmask of policy->cpus field to
> trace_cpu_frequency(). This way we maintain backwards compatibility:
> trace_cpu_frequency() is not removed, and its pre-existing fields are
> not disturbed.
> 
> Call flow wise, we can delete all the for_each_cpu() loops, and we
> still retain the benefits of the trace emitting once per policy
> instead of once per cpu.

Fine by me. I have added Scheduler maintainers in the loop to see if they have a
different view.

-- 
viresh