Re: [PATCH] softirq,tracing: enable to trace softirq raise latency

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

* Lai Jiangshan (laijs@cn.fujitsu.com) wrote:
> 
> Add a tracepoint for tracing when softirq action is raised.
> 
> It and the existed tracepoints complete softirq's tracepoints:
> softirq_raise, softirq_entry and softirq_exit.
> 
> And when this tracepoint is used in combination with
> the softirq_entry tracepoint we can determine
> the softirq raise latency.
> 

Hi Lai,

It generally looks good, we have a similar instrumentation point in the
LTTng tree, and it's really useful. It's a good idea to instrument
__raise_softirq_irqoff rather than just raise_softirq_irqoff: it
includes the HI/TASKLET and HRTIMER softirqs.

There is just a small comment which should probably also be changed,
please see below, besides that, you have my

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 75f3f00..b368d5d 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -18,6 +18,7 @@
>  #include <asm/atomic.h>
>  #include <asm/ptrace.h>
>  #include <asm/system.h>
> +#include <trace/events/irq.h>
>  
>  /*
>   * These correspond to the IORESOURCE_IRQ_* defines in
> @@ -372,7 +373,13 @@ 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);
> -#define __raise_softirq_irqoff(nr) do { or_softirq_pending(1UL << (nr)); } while (0)
> +
> +static inline void __raise_softirq_irqoff(unsigned int nr)
> +{
> +	trace_softirq_raise(nr);
> +	or_softirq_pending(1UL << nr);
> +}
> +
>  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 dcfcd44..799af09 100644
> --- a/include/trace/events/irq.h
> +++ b/include/trace/events/irq.h
> @@ -5,7 +5,9 @@
>  #define _TRACE_IRQ_H
>  
>  #include <linux/tracepoint.h>
> -#include <linux/interrupt.h>
> +
> +struct irqaction;
> +struct softirq_action;
>  
>  #define softirq_name(sirq) { sirq##_SOFTIRQ, #sirq }
>  #define show_softirq_name(val)				\
> @@ -83,6 +85,32 @@ TRACE_EVENT(irq_handler_exit,
>  );
>  
>  /**
> + * softirq_raise - called immediately when a softirq is raised
> + * @nr: softirq vector number
> + *
> + * Tracepoint for tracing when softirq action is raised.
> + * Also, when used in combination with the softirq_entry tracepoint
> + * we can determine the softirq raise latency.
> + */
> +TRACE_EVENT(softirq_raise,
> +
> +	TP_PROTO(unsigned int nr),
> +
> +	TP_ARGS(nr),
> +
> +	TP_STRUCT__entry(
> +		__field(	unsigned int,	vec		)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->vec	= nr;
> +	),
> +
> +	TP_printk("vec=%d [action=%s]", __entry->vec,
> +		  show_softirq_name(__entry->vec))
> +);
> +
> +/**
>   * softirq_entry - called immediately before the softirq handler
>   * @h: pointer to struct softirq_action
>   * @vec: pointer to first struct softirq_action in softirq_vec array

Please change this comment to "@vec: softirq vector number" while you
are at it. The same probably needs to be done for softirq_exit. @vec are
not pointers: these are offsets.

Thanks,

Mathieu


> @@ -100,11 +128,11 @@ TRACE_EVENT(softirq_entry,
>  	TP_ARGS(h, vec),
>  
>  	TP_STRUCT__entry(
> -		__field(	int,	vec			)
> +		__field(	unsigned int,	vec		)
>  	),
>  
>  	TP_fast_assign(
> -		__entry->vec = (int)(h - vec);
> +		__entry->vec = (unsigned int)(h - vec);
>  	),
>  
>  	TP_printk("vec=%d [action=%s]", __entry->vec,
> @@ -129,11 +157,11 @@ TRACE_EVENT(softirq_exit,
>  	TP_ARGS(h, vec),
>  
>  	TP_STRUCT__entry(
> -		__field(	int,	vec			)
> +		__field(	unsigned int,	vec		)
>  	),
>  
>  	TP_fast_assign(
> -		__entry->vec = (int)(h - vec);
> +		__entry->vec = (unsigned int)(h - vec);
>  	),
>  
>  	TP_printk("vec=%d [action=%s]", __entry->vec,
> 

-- 
Mathieu Desnoyers
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