linux-kernel - Re: [PATCH v3] ftrace: add a tracepoint for __raise_softirq

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Message-ID: <4A07D3B3.10605@cn.fujitsu.com>
Date:	Mon, 11 May 2009 15:28:51 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, fweisbec@...il.com,
	rostedt@...dmis.org, zhaolei@...fujitsu.com, laijs@...fujitsu.com,
	Li Zefan <lizf@...fujitsu.com>
Subject: Re: [PATCH v3] ftrace: add a tracepoint for	__raise_softirq_irqoff()



Mathieu Desnoyers wrote:
> * Xiao Guangrong (xiaoguangrong@...fujitsu.com) wrote:
>> From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
>>

>> +#ifdef CONFIG_TRACEPOINTS
>> +extern void __raise_softirq_irqoff(unsigned int nr);
>> +#else
>>  #define __raise_softirq_irqoff(nr) do { or_softirq_pending(1UL << (nr)); } while (0)
> 
> Can you put the 
> 	trace_irq_softirq_raise(nr);
> 
> directly in the define rather than adding this weird CONFIG_TRACEPOINTS?
> (and change the define for a static inline), something like :
> 
> static inline void __raise_softirq_irqoff(unsigned int nr)
> {
> 	trace_irq_softirq_raise(nr);
> 	or_softirq_pending(1UL << (nr);
> }
> 
> This would ensure we don't add a function call on the
> __raise_softirq_irqoff() fast-path.
> 

We did this in v2, and we think it is better for same reason.
But ...

> Beware of circular include dependencies though. The tracepoints are
> meant not to have this kind of problems (I try to keep the dependencies
> very minimalistic), but I wonder if Steven's TRACE_EVENT is now ok on
> this aspect.
> 

We encount this type of problem in v2.
So we move to this version(v3).

> If TRACE_EVENT happens to pose problems with circular header
> dependencies, then try moving to the DECLARE_TRACE/DEFINE_TRACE scheme
> which has been more thoroughly tested as a first step.
> 

IMHO, TRACE_EVENT framework is better for its more generic as ingo said,
and it also provide ftrace support which means user can view tracepoint
information from /debug/tracing/events.

Although this TRACE_EVENT happens to expose problems with circular header
dependencies, we should not refuse using TRACE_EVENT, instead we should
try to fix it for the whole TRACE_EVENT facility later.

Thanks

> Mathieu
> 
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