Re: [PATCH] tasklet: Introduce tasklet tracepoints

[Steven Rostedt]

On Sat,  5 Sep 2020 14:04:12 +0800
Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:

> Introduce tracepoints for tasklets just like softirq does. In this case,
> we can calculate tasklet latency and know what tasklet run.
> 
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>  include/trace/events/irq.h | 44 ++++++++++++++++++++++++++++++++++++++
>  kernel/softirq.c           |  2 ++
>  2 files changed, 46 insertions(+)
> 
> diff --git a/include/trace/events/irq.h b/include/trace/events/irq.h
> index eeceafaaea4c..69a16f3a21c2 100644
> --- a/include/trace/events/irq.h
> +++ b/include/trace/events/irq.h
> @@ -160,6 +160,50 @@ DEFINE_EVENT(softirq, softirq_raise,
>  	TP_ARGS(vec_nr)
>  );
>  
> +DECLARE_EVENT_CLASS(tasklet,
> +
> +	TP_PROTO(struct tasklet_struct *t),
> +
> +	TP_ARGS(t),
> +
> +	TP_STRUCT__entry(
> +		__field(	void *,	callback	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->callback = t->callback;

I think you need to replicate the logic in the code:

		if (t->use_callback)
			__entry->callback = t->callback;
		else
			__entry->callback = t->func;

-- Steve

> +	),
> +
> +	TP_printk("callback=%ps", __entry->callback)
> +);
> +
> +/**
> + * tasklet_entry - called immediately before the tasklet handler
> + * @t: pointer to struct tasklet_struct
> + *
> + * When used in combination with the tasklet_exit tracepoint
> + * we can determine the tasklet handler routine.
> + */
> +DEFINE_EVENT(tasklet, tasklet_entry,
> +
> +	TP_PROTO(struct tasklet_struct *t),
> +
> +	TP_ARGS(t)
> +);
> +
> +/**
> + * tasklet_exit - called immediately after the tasklet handler returns
> + * @t: pointer to struct tasklet_struct
> + *
> + * When used in combination with the tasklet_entry tracepoint
> + * we can determine the tasklet handler routine.
> + */
> +DEFINE_EVENT(tasklet, tasklet_exit,
> +
> +	TP_PROTO(struct tasklet_struct *t),
> +
> +	TP_ARGS(t)
> +);
>  #endif /*  _TRACE_IRQ_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index bf88d7f62433..0f9f5b2cc3d3 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -553,10 +553,12 @@ static void tasklet_action_common(struct softirq_action *a,
>  				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
>  							&t->state))
>  					BUG();
> +				trace_tasklet_entry(t);
>  				if (t->use_callback)
>  					t->callback(t);
>  				else
>  					t->func(t->data);
> +				trace_tasklet_exit(t);
>  				tasklet_unlock(t);
>  				continue;
>  			}