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

Mathieu Desnoyers
2009-05-05T16:16:24Z

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