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

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Date:	Wed, 27 May 2009 12:10:58 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
cc:	mingo@...e.hu, LKML <linux-kernel@...r.kernel.org>,
	Zhaolei <zhaolei@...fujitsu.com>, kosaki.motohiro@...fujitsu.com,
	Steven Rostedt <rostedt@...dmis.org>, fweisbec@...il.com
Subject: Re: [PATCH 1/3] ftrace: add tracepoint for timer

On Wed, 27 May 2009, Xiao Guangrong wrote:
> >> +	TP_printk("timer=%p func=%pf expires=%lu cpu=%d", __entry->timer,
> >> +		  __entry->function, __entry->expires, __entry->cpu)
> >> +);
> > 
> >   How do we connect the trace to the jiffies value when the timer
> >   was started ?
> > 
> 
> ftrace already have time information in trace event's output, we can use it instead

  Hmm, I'm not sure whether we can see the jiffies value there, but ok. 
 
> >> @@ -547,6 +550,7 @@ void init_timer_key(struct timer_list *timer,
> >>  {
> >>  	debug_timer_init(timer);
> >>  	__init_timer(timer, name, key);
> >> +	trace_timer_init(timer);
> > 
> >   Can we please avoid to have two debug calls in one 2 line function ?
> > 
> 
> debug_timer_init() must call before object's init, but tracepoint have to call
> after object's init beacuse if we move the tracepoint to before object init, the
> object has no data yet.

  Err.

> >> + TRACE_EVENT(timer_init,
> >> +
> >> + TP_PROTO(struct timer_list *timer),
> >> +
> >> + TP_ARGS(timer),
> >> +
> >> + TP_STRUCT__entry(
> >> + __field( void *, timer )
> >> + ),
> >> +
> >> + TP_fast_assign(
> >> + __entry->timer = timer;
> >> + ),
> >> +
> >> + TP_printk("timer=%p", __entry->timer)
> >> +);

  Is timer different before and after the __init_timer call ?
 
> >>  }
> >>  EXPORT_SYMBOL(init_timer_key);
> >>  
> >> @@ -565,6 +569,7 @@ static inline void detach_timer(struct timer_list *timer,
> >>  	struct list_head *entry = &timer->entry;
> >>  
> >>  	debug_timer_deactivate(timer);
> >> +	trace_timer_cancel(timer);
> > 
> >   Ditto. Please create one debug entity which covers both.
> >
> 
> IMHO, we can't create one entity for init event, so we do better detach other event.

  See above.
 
Thanks,

	tglx
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