linux-kernel - Re: [PATCH v2 1/3] ftrace: add tracepoint for timer

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Message-ID: <alpine.LFD.2.00.0907062140010.19480@localhost.localdomain>
Date:	Mon, 6 Jul 2009 22:08:52 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Zhaolei <zhaolei@...fujitsu.com>, kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] ftrace: add tracepoint for timer

On Mon, 6 Jul 2009, Xiao Guangrong wrote:
> Changelog v1->v2:
> 1: Add jiffies info into timer
> 2: Combine debugobjects and trace as Thomas's suggestion

I like it that way. Some minor nitpicks below.
 
> +TRACE_EVENT(timer_expire,
> +
> +	TP_PROTO(struct timer_list *timer),
> +
> +	TP_ARGS(timer),
> +
> +	TP_STRUCT__entry(
> +		__field( void *,	timer		)
> +		__field( void *,	function	)

  Do we really need the function here? It does not change between
  start and expiry.

> +TRACE_EVENT(timer_cancel,
> +
> +	TP_PROTO(struct timer_list *timer),
> +
> +	TP_ARGS(timer),
> +
> +	TP_STRUCT__entry(
> +		__field( void *,	timer		)
> +		__field( void *,	function	)

  Ditto.

> +
> +static inline void debug_and_trace_timer_expire(struct timer_list *timer)

  Technically not really necessary. The debug code does not care about
  it.

>  			timer = list_first_entry(head, struct timer_list,entry);
> +			debug_and_trace_timer_expire(timer);
>  			fn = timer->function;
>  			data = timer->data;
>  

Can you please add the tracepoint which was suggested by Anton (IIRC)
which allows us to measure the execution time of the callback function
? There is no need to dereference timer in the expiry tracepoint, we
just store the pointer. So we can safely move the tracepoints just
around the function call.

   trace_timer_expire(timer);
   fn(data);
   trace_timer_callback_done(timer);

Or whatever fancy name you come up with.

Thanks,

	tglx
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