linux-kernel - Re: [PATCH v2] cpufreq: trace frequency limits change

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Message-ID: <20180724172405.GA257870@joelaf.mtv.corp.google.com>
Date:   Tue, 24 Jul 2018 10:24:05 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Ruchi Kandoi <kandoiruchi@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH v2] cpufreq: trace frequency limits change

On Tue, Jul 24, 2018 at 09:49:32AM -0400, Steven Rostedt wrote:
> On Fri, 20 Jul 2018 15:21:14 -0700
> Joel Fernandes <joel@...lfernandes.org> wrote:
> 
> > From: Ruchi Kandoi <kandoiruchi@...gle.com>
> > 
> > systrace used for tracing for Android systems has carried a patch for
> > many years in the Android tree that traces when the cpufreq limits
> > change.  With the help of this information, systrace can know when the
> > policy limits change and can visually display the data. Lets add
> > upstream support for the same.
> > 
> > Signed-off-by: Ruchi Kandoi <kandoiruchi@...gle.com>
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > ---
> > v1->v2: Minor changes suggested by Viresh
> > 
> >  Documentation/trace/events-power.rst |  1 +
> >  drivers/cpufreq/cpufreq.c            |  1 +
> >  include/trace/events/power.h         | 25 +++++++++++++++++++++++++
> >  3 files changed, 27 insertions(+)
> > 
> > diff --git a/Documentation/trace/events-power.rst b/Documentation/trace/events-power.rst
> > index a77daca75e30..2ef318962e29 100644
> > --- a/Documentation/trace/events-power.rst
> > +++ b/Documentation/trace/events-power.rst
> > @@ -27,6 +27,7 @@ cpufreq.
> >  
> >    cpu_idle		"state=%lu cpu_id=%lu"
> >    cpu_frequency		"state=%lu cpu_id=%lu"
> > +  cpu_frequency_limits	"min=%lu max=%lu cpu_id=%lu"
> >  
> >  A suspend event is used to indicate the system going in and out of the
> >  suspend mode:
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index b0dfd3222013..4fd935df101e 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -2236,6 +2236,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
> >  
> >  	policy->min = new_policy->min;
> >  	policy->max = new_policy->max;
> > +	trace_cpu_frequency_limits(policy->min, policy->max, policy->cpu);
> 
> Wouldn't it make more sense just to pass in "policy"?

Yes I agree, good idea.

> >  
> >  	policy->cached_target_freq = UINT_MAX;
> >  
> > diff --git a/include/trace/events/power.h b/include/trace/events/power.h
> > index 908977d69783..f5bec45108b6 100644
> > --- a/include/trace/events/power.h
> > +++ b/include/trace/events/power.h
> > @@ -148,6 +148,31 @@ DEFINE_EVENT(cpu, cpu_frequency,
> >  	TP_ARGS(frequency, cpu_id)
> >  );
> >  
> > +TRACE_EVENT(cpu_frequency_limits,
> > +
> > +	TP_PROTO(unsigned int min_freq, unsigned int max_freq,
> > +		unsigned int cpu_id),
> > +
> > +	TP_ARGS(min_freq, max_freq, cpu_id),
> > +
> > +	TP_STRUCT__entry(
> > +		__field(u32, min_freq)
> > +		__field(u32, max_freq)
> > +		__field(u32, cpu_id)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->min_freq = min_freq;
> > +		__entry->max_freq = max_freq;
> > +		__entry->cpu_id = cpu_id;
> 
> Then have here:
> 
> 		__entry->min_freq = policy->min;
> 		__entry->max_freq = policy->max;
> 		__entry->puc_id = policy->cpu;
> 
> It would also make the footprint of the tracepoint in the code smaller
> as it would pass fewer parameters to the trace event.

Yes, that's a great idea. I'll make the change and post v3.

-Joel