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

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Message-ID: <20190212181415.1156e542@gandalf.local.home>
Date:   Tue, 12 Feb 2019 18:14:15 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Lukasz Luba <l.luba@...tner.samsung.com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        b.zolnierkie@...sung.com, myungjoo.ham@...sung.com,
        cw00.choi@...sung.com, kyungmin.park@...sung.com,
        m.szyprowski@...sung.com, s.nawrocki@...sung.com, tkjos@...gle.com,
        joel@...lfernandes.org, chris.diamand@....com, mka@...omium.org,
        mingo@...hat.com
Subject: Re: [PATCH v3 6/7] trace: events: add devfreq trace event file

On Tue, 12 Feb 2019 23:23:57 +0100
Lukasz Luba <l.luba@...tner.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@...tner.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@...sung.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 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)

-- Steve

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