Re: [PATCH v3] ftrace: add a tracepoint for __raise_softirq_irqoff()

Xiao Guangrong
2009-05-11T07:28:20Z

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