linux-kernel - Re: [PATCH] sched/cpufreq: Align trace event behavior of fast switching

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Date:   Mon, 26 Aug 2019 11:40:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Douglas RAILLARD <douglas.raillard@....com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        viresh.kumar@...aro.org, mingo@...hat.com
Subject: Re: [PATCH] sched/cpufreq: Align trace event behavior of fast
 switching

On Mon, Aug 26, 2019 at 11:10:52AM +0200, Rafael J. Wysocki wrote:
> On Wednesday, August 7, 2019 5:33:40 PM CEST Douglas RAILLARD wrote:
> > Fast switching path only emits an event for the CPU of interest, whereas the
> > regular path emits an event for all the CPUs that had their frequency changed,
> > i.e. all the CPUs sharing the same policy.
> > 
> > With the current behavior, looking at cpu_frequency event for a given CPU that
> > is using the fast switching path will not give the correct frequency signal.
> > 
> > Signed-off-by: Douglas RAILLARD <douglas.raillard@....com>
> > ---
> >  kernel/sched/cpufreq_schedutil.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 1f82ab108bab..975ccc3de807 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -153,6 +153,7 @@ static void sugov_fast_switch(struct sugov_policy *sg_policy, u64 time,
> >  			      unsigned int next_freq)
> >  {
> >  	struct cpufreq_policy *policy = sg_policy->policy;
> > +	int cpu;
> >  
> >  	if (!sugov_update_next_freq(sg_policy, time, next_freq))
> >  		return;
> > @@ -162,7 +163,11 @@ static void sugov_fast_switch(struct sugov_policy *sg_policy, u64 time,
> >  		return;
> >  
> >  	policy->cur = next_freq;
> > -	trace_cpu_frequency(next_freq, smp_processor_id());
> > +
> > +	if (trace_cpu_frequency_enabled()) {
> > +		for_each_cpu(cpu, policy->cpus)
> > +			trace_cpu_frequency(next_freq, cpu);
> > +	}
> >  }
> >  
> >  static void sugov_deferred_update(struct sugov_policy *sg_policy, u64 time,
> > 
> 
> Peter, any comments here?

I was thinking this would be a static map and dealing with it would be
something trivially done in post (or manually while reading), but sure,
whatever:

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>