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

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Date:	Fri, 29 May 2009 10:00:37 +0800
From:	Zhaolei <zhaolei@...fujitsu.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>, mingo@...e.hu,
	LKML <linux-kernel@...r.kernel.org>,
	kosaki.motohiro@...fujitsu.com,
	Steven Rostedt <rostedt@...dmis.org>, fweisbec@...il.com
Subject: Re: Re: [PATCH 1/3] ftrace: add tracepoint for timer

Thomas Gleixner wrote:
> 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 ?

Hello, Thomas

Yes, timer's pointer is same before and after __init_timer().
We don't need to put debug_timer_init() and trace_timer_init() into different
place.

But, for trace_timer_start() in __mod_timer(), we need to put it after
timer->* changed.
Nevertheless, it don't means we need separate trace_timer_start() and
debug_timer_activate(), because we can put move debug_timer_activate() below,
as:
-	debug_timer_activate(timer);
	...
 	timer->expires = expires;
 	internal_add_timer(base, timer);
+	debug_timer_activate(timer);
+	trace_timer_start(timer, smp_processor_id());

Then we can also combine debug_timer_activate() and trace_timer_start() into
one function.

So we'll do what you suggested.

Thanks
Zhaolei

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