linux-kernel - Re: [PATCH v2] devfreq: Add tracepoint for frequency changes

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Date:   Tue, 24 Sep 2019 12:37:21 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Chanwoo Choi <cw00.choi@...sung.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH v2] devfreq: Add tracepoint for frequency changes

On Fri, Sep 20, 2019 at 10:15:57AM +0900, Chanwoo Choi wrote:
> Hi,

sorry for the delayed response, you message got buried in my
mailbox.

> On 19. 9. 20. 오전 2:44, Matthias Kaehlcke wrote:
> > Add a tracepoint for frequency changes of devfreq devices and
> > use it.
> > 
> > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > ---
> > (sending v2 without much delay wrt v1, since the change in devfreq
> >  probably isn't controversial, and I'll be offline a few days)
> > 
> > Changes in v2:
> > - included trace_devfreq_frequency_enabled() in the condition
> >   to avoid unnecessary evaluation when the trace point is
> >   disabled
> > ---
> >  drivers/devfreq/devfreq.c      |  3 +++
> >  include/trace/events/devfreq.h | 18 ++++++++++++++++++
> >  2 files changed, 21 insertions(+)
> > 
> > diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> > index ab22bf8a12d6..e9f04dcafb01 100644
> > --- a/drivers/devfreq/devfreq.c
> > +++ b/drivers/devfreq/devfreq.c
> > @@ -317,6 +317,9 @@ static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
> >  
> >  	devfreq->previous_freq = new_freq;
> >  
> > +	if (trace_devfreq_frequency_enabled() && new_freq != cur_freq)
> > +		trace_devfreq_frequency(devfreq, new_freq);
> 
> You can change as following without 'new_freq' variable
> because devfreq->previous_freq is the new frequency.	
> 	trace_devfreq_frequency(devfreq);

In general that sounds good.

devfreq essentially uses df->previous_freq as df->cur_freq, I think
most code using it would be clearer if we renamed it accordingly.
I'll send a separate patch for this.

> > +
> >  	if (devfreq->suspend_freq)
> >  		devfreq->resume_freq = cur_freq;
> >  
> > diff --git a/include/trace/events/devfreq.h b/include/trace/events/devfreq.h
> > index cf5b8772175d..a62d32fe3c33 100644
> > --- a/include/trace/events/devfreq.h
> > +++ b/include/trace/events/devfreq.h
> > @@ -8,6 +8,24 @@
> >  #include <linux/devfreq.h>
> >  #include <linux/tracepoint.h>
> >  
> > +TRACE_EVENT(devfreq_frequency,
> > +	TP_PROTO(struct devfreq *devfreq, unsigned long freq),
> 
> 'unsigned long freq' parameter is not necessary.
> 
> > +
> > +	TP_ARGS(devfreq, freq),
> > +
> > +	TP_STRUCT__entry(
> > +		__string(dev_name, dev_name(&devfreq->dev))
> > +		__field(unsigned long, freq)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__assign_str(dev_name, dev_name(&devfreq->dev));
> > +		__entry->freq = freq;
> 
> Initialize the new frequency with 'devfreq->previous_freq' as following:
> 
> 		__entry->freq = devfreq->previous_freq;
> 
> > +	),
> > +
> > +	TP_printk("dev_name=%s freq=%lu", __get_str(dev_name), __entry->freq)
> > +);
> > +
> >  TRACE_EVENT(devfreq_monitor,
> >  	TP_PROTO(struct devfreq *devfreq),
> >  
> > 
> 
> 
> -- 
> Best Regards,
> Chanwoo Choi
> Samsung Electronics