Re: [PATCH v3 6/7] trace: events: add devfreq trace event file

From: Lukasz Luba <l.luba@partner.samsung.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	b.zolnierkie@samsung.com, myungjoo.ham@samsung.com,
	cw00.choi@samsung.com, kyungmin.park@samsung.com,
	m.szyprowski@samsung.com, s.nawrocki@samsung.com,
	tkjos@google.com, joel@joelfernandes.org, chris.diamand@arm.com,
	mka@chromium.org, mingo@redhat.com
Subject: Re: [PATCH v3 6/7] trace: events: add devfreq trace event file
Date: Wed, 13 Feb 2019 14:35:01 +0100	[thread overview]
Message-ID: <fb5d5359-7663-f119-f28f-7be820e1108d@partner.samsung.com> (raw)
In-Reply-To: <20190212181415.1156e542@gandalf.local.home>

Hi Steven,

On 2/13/19 12:14 AM, Steven Rostedt wrote:
> On Tue, 12 Feb 2019 23:23:57 +0100
> Lukasz Luba <l.luba@partner.samsung.com> wrote:
> 
>> The patch adds a new file for with trace events for devfreq
>> framework. They are used for performance analysis of the framework.
>> It also contains updates in MAINTAINERS file adding new entry for
>> devfreq maintainers.
>>
>> Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
>> ---
>>   MAINTAINERS                    |  1 +
>>   include/trace/events/devfreq.h | 39 +++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 40 insertions(+)
>>   create mode 100644 include/trace/events/devfreq.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 9919840..c042fda 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -4447,6 +4447,7 @@ S:	Maintained
>>   F:	drivers/devfreq/
>>   F:	include/linux/devfreq.h
>>   F:	Documentation/devicetree/bindings/devfreq/
>> +F:	include/trace/events/devfreq.h
>>   
>>   DEVICE FREQUENCY EVENT (DEVFREQ-EVENT)
>>   M:	Chanwoo Choi <cw00.choi@samsung.com>
>> diff --git a/include/trace/events/devfreq.h b/include/trace/events/devfreq.h
>> new file mode 100644
>> index 0000000..fec9304
>> --- /dev/null
>> +++ b/include/trace/events/devfreq.h
>> @@ -0,0 +1,39 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#undef TRACE_SYSTEM
>> +#define TRACE_SYSTEM devfreq
>> +
>> +#if !defined(_TRACE_DEVFREQ_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_DEVFREQ_H
>> +
>> +#include <linux/devfreq.h>
>> +#include <linux/tracepoint.h>
>> +
>> +TRACE_EVENT(devfreq_monitor,
>> +	TP_PROTO(const char *dev_name, unsigned long freq,
>> +		 unsigned int polling_ms, unsigned long busy_time,
>> +		 unsigned long total_time),
>> +
>> +	TP_ARGS(dev_name, freq, polling_ms, busy_time, total_time),
>> +
>> +	TP_STRUCT__entry(
>> +		__string(dev_name, dev_name)
>> +		__field(unsigned long, freq)
>> +		__field(unsigned int, polling_ms)
>> +		__field(unsigned int, load)
>> +	),
>> +
>> +	TP_fast_assign(
>> +		__assign_str(dev_name, dev_name);
>> +		__entry->freq = freq;
>> +		__entry->polling_ms = polling_ms;
>> +		__entry->load = (100 * busy_time) / total_time;
> 
> How critical is the code that this trace event is called in. If it is
> not that critical (it is a slow path), then this is fine, but if this
> is not a slow path (something triggered 100 HZ or less), then I would
> recommend moving the above calculation to TP_printk(). A divide is a
> slow operation, and is best to do that in the post processing. The
> current location does the divide at the time of the tracepoint is
> called.
I wasn't aware of these two stages, good to know.
I will move it to TP_printk().
> 
> I would also have a check to make sure that total_time is not zero
> here, otherwise that could be bad.
> 
> 		__entry->busy_time = busy_time;
> 		__entry->total_time = total_time;
> 

>> +	),
>> +
>> +	TP_printk("dev_name=%s freq=%lu polling_ms=%u load=%u",
> 
> 
>> +		__get_str(dev_name), __entry->freq, __entry->polling_ms,
> 
> 		__entry->total_time == 0 ? 100 :
> 			__entry->busy_time / __entry->total_time)
Thank you for the review.
I will add this check.

Regards,
Lukasz
> 
> -- Steve
> 
>> +		__entry->load)
>> +);
>> +#endif /* _TRACE_DEVFREQ_H */
>> +
>> +/* This part must be outside protection */
>> +#include <trace/define_trace.h>
> 
> 
> 