Re: [PATCH 4/4] sched: add trace event for idle injection

[Javi Merino <javi.merino@arm.com>]

[ CCing Steve Rostedt for the tracing bits ]

On Fri, Nov 13, 2015 at 11:53:07AM -0800, Jacob Pan wrote:
> Trace events for idle injection can be used to determine
> timer activities for checking synchronization. In addition they
> also helps to determine when the runqueue is throttled.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>  include/linux/sched.h        |  5 +++++
>  include/trace/events/sched.h | 25 +++++++++++++++++++++++++
>  kernel/sched/fair.c          |  3 +++
>  3 files changed, 33 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index ff551a3..99c79bf 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -3189,6 +3189,11 @@ extern int proc_sched_cfs_idle_inject_duration_handler(struct ctl_table *table,
>  						int write,
>  						void __user *buffer,
>  						size_t *length, loff_t *ppos);
> +enum cfs_idle_inject_action {
> +	CFS_IDLE_INJECT_TIMER,    /* timer sync point */
> +	CFS_IDLE_INJECT_FORCED,   /* idle forced in rq */
> +	CFS_IDLE_INJECT_YIELD_SOFTIRQ   /* yield to pending softirq */
> +};
>  #endif
>  
>  #endif
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index 539d6bc..52c11c1 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -566,6 +566,31 @@ TRACE_EVENT(sched_wake_idle_without_ipi,
>  
>  	TP_printk("cpu=%d", __entry->cpu)
>  );
> +
> +#ifdef CONFIG_CFS_IDLE_INJECT
> +/*
> + * Tracepoint for idle injection
> + */
> +TRACE_EVENT(sched_cfs_idle_inject,
> +
> +	TP_PROTO(enum cfs_idle_inject_action action, int throttled),
> +
> +	TP_ARGS(action, throttled),
> +
> +	TP_STRUCT__entry(
> +		__field(enum cfs_idle_inject_action, action)
> +		__field(int, throttled)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->action = action;
> +		__entry->throttled = throttled;
> +	),
> +
> +	TP_printk("action:%d throttled:%d", __entry->action, __entry->throttled)
> +);
> +#endif
> +

One minor nit: can you use key=value (i.e. "throttled=%d") instead for
consistency with the rest of this file?

Other than that, I know that Peter suggested an enum for the action,
but wouldn't it be better to create an EVENT_CLASS and subclass the
three actions from it?  Something like:

DECLARE_EVENT_CLASS(sched_cfs_idle_inject_template,

	TP_PROTO(int throttled),

	TP_ARGS(throttled),

	TP_STRUCT__entry(
		__field(int, throttled)
	),

	TP_fast_assign(
		__entry->throttled = throttled;
	),

	TP_printk("throttled=%d", __entry->throttled)
);

DEFINE_EVENT(sched_cfs_idle_inject_template, sched_cfs_idle_inject_timer,
	     TP_PROTO(int throttled),
	     TP_ARGS(throttled));

DEFINE_EVENT(sched_cfs_idle_inject_template, sched_cfs_idle_inject_forced,
	     TP_PROTO(int throttled),
	     TP_ARGS(throttled));

DEFINE_EVENT(sched_cfs_idle_inject_template,
	     sched_cfs_idle_inject_yield_softirq,
	     TP_PROTO(int throttled),
	     TP_ARGS(throttled));

>  #endif /* _TRACE_SCHED_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a0cd777..20027eb 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5248,8 +5248,10 @@ idle:
>  	if (in_forced_idle(cfs_rq)) {
>  		if (unlikely(local_softirq_pending())) {
>  			__unthrottle_cfs_rq(cfs_rq);
> +			trace_sched_cfs_idle_inject(CFS_IDLE_INJECT_YIELD_SOFTIRQ, 1);

This becomes:

			trace_sched_cfs_idle_inject_yield_softirq(1);

>  			goto again;
>  		}
> +		trace_sched_cfs_idle_inject(CFS_IDLE_INJECT_FORCED, 1);

This becomes:
		trace_sched_cfs_idle_inject_forced(1);

>  		return NULL;
>  	}
>  	/*
> @@ -8432,6 +8434,7 @@ static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *hrtimer)
>  		throttle_rq(cpu);
>  	}
>  	raw_cpu_write(idle_injected, !status);
> +	trace_sched_cfs_idle_inject(CFS_IDLE_INJECT_TIMER, !status);

and this would be:

	trace_sched_cfs_idle_inject_timer(!status);

>  
>  	return HRTIMER_RESTART;
>  }

Cheers,
Javi