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

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Date:	Tue, 5 May 2009 12:16:05 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
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()

* Xiao Guangrong (xiaoguangrong@...fujitsu.com) wrote:
> From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> 
> This patch is modified from Mathieu Desnoyers' patch. The original patch
> can be found here: 
> 	http://marc.info/?l=linux-kernel&m=123791201816245&w=2
> This tracepoint can trace the time stamp when softirq action is raised. 
> 
> Changelog for v1 -> v2: 
> 1: Use TRACE_EVENT instead of DEFINE_TRACE
> 2: Move the tracepoint from raise_softirq_irqoff() to
>    __raise_softirq_irqoff()
> 
> Changelog for v2 -> v3: 
> Move the definition of __raise_softifq_irqoff() to .c file when
> CONFIG_TRACEPOINTS is enabled, to avoid recursive includes
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> 
> ---
>  include/linux/interrupt.h  |    6 ++++++
>  include/trace/events/irq.h |   18 ++++++++++++++++++
>  kernel/softirq.c           |    8 ++++++++
>  3 files changed, 32 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index dd574d5..3143341 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -361,7 +361,13 @@ asmlinkage void do_softirq(void);
>  asmlinkage void __do_softirq(void);
>  extern void open_softirq(int nr, void (*action)(struct softirq_action *));
>  extern void softirq_init(void);
> +
> +#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.

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.

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.

Mathieu

> +#endif
> +
>  extern void raise_softirq_irqoff(unsigned int nr);
>  extern void raise_softirq(unsigned int nr);
>  extern void wakeup_softirqd(void);
> diff --git a/include/trace/events/irq.h b/include/trace/events/irq.h
> index 32a9f7e..3c895bb 100644
> --- a/include/trace/events/irq.h
> +++ b/include/trace/events/irq.h
> @@ -128,6 +128,24 @@ TRACE_EVENT(softirq_exit,
>  	TP_printk("softirq=%d action=%s", __entry->vec, __get_str(name))
>  );
>  
> +TRACE_EVENT(irq_softirq_raise,
> +
> +	TP_PROTO(unsigned int nr),
> +
> +	TP_ARGS(nr),
> +
> +	TP_STRUCT__entry(
> +		__field(	unsigned int,	nr	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->nr	= nr;
> +	),
> +
> +	TP_printk("softirq=%d action=%s is raised",
> +		__entry->nr, softirq_to_name[__entry->nr])
> +);
> +
>  #endif /*  _TRACE_IRQ_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index b41fb71..bd0546b 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -310,6 +310,14 @@ void irq_exit(void)
>  	preempt_enable_no_resched();
>  }
>  
> +#ifdef CONFIG_TRACEPOINTS
> +inline void __raise_softirq_irqoff(unsigned int nr)
> +{
> +	trace_irq_softirq_raise(nr);
> +	or_softirq_pending(1UL << (nr));
> +}
> +#endif
> +
>  /*
>   * This function must run with irqs disabled!
>   */
> -- 
> 1.6.1.2
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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