linux-kernel - Re: [PATCH 0/3] ftrace: add tracepoint for timer event

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Message-ID: <4A1CCD84.2040607@cn.fujitsu.com>
Date:	Wed, 27 May 2009 13:20:04 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	mingo@...e.hu, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	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 0/3] ftrace: add tracepoint for timer event



Thomas Gleixner wrote:
> On Fri, 22 May 2009, Xiao Guangrong wrote:
>> We already have debugobject in timer to init/activate/deactivate/free,
>> but it can't be covered function of there tracepoints, because:
>> 1: We can't get timer's lifecycle information in userspace by debugobject,
>>    it is necessary for system engineer to investigate system trouble caused
>>    by using timer.
>> 2: We can't get information of whole lifecycle of timer by debugobject, 
>>    for example, deactivation of a timer.
>> 3: There are many different tracing code in many kernel subsystem as
>>    blktrace, debugobject, and tracepoint is designed as generic way
>>    to unify these tracing way.
> 
> No. You can not unify debugobject into tracepoints. debugobjects is a
> totally different beast. It's main purpose is to prevent undebugable
> system crashes which we have seen several times e.g: freeing of an
> active timer, reinitializing of an active timer ...
> 
> Dealing with these problems is not covered by tracepoints by any
> means. The trace point does not prevent the system crash which happens
> 2 seconds after the fact that an active timer is kfree'd, debugobject
> does and it points you to the exact place where the shit happens.
> 
> I'm not opposed to add tracepoints to the timer code at all. In fact I
> appreciate that, but your idea of substituting debugobjects with
> tracing is just plain wrong.
> 
> It's the other way round. tracing can reuse the existing debugobject
> hooks to insert trace points, but it can not replace the functionality
> at all.
> 

Hello tglx:
Thanks for you review!

Totally agree.
Actually I do know the difference between debugobject and tracepoint. Sorry
for making you misunderstand what I said for my pool English.

Thanks,
Xiao Guangrong

> 	tglx
> 
> 
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