Re: [PATCH 4/5] sched: Add rt task enqueue/dequeue trace points

[Gabriele Monaco]

On Wed, 2025-07-30 at 14:45 +0200, Nam Cao wrote:
> Add trace points into enqueue_task_rt() and dequeue_task_rt(). They
> are useful to implement RV monitor which validates RT scheduling.
> 

I get it's much simpler this way, but is it that different to follow
the task's existing tracepoints?

* task going to sleep (switch:prev_state != RUNNING) is dequeued
* task waking up is enqueued
* changing the tasks's policy (setpolicy and setattr syscalls) should
enqueue/dequeue as well

This is more thinking out loud, but I'm doing right now something
rather similar with the deadline tasks and this seems reasonable, at
least on paper.

What do you think?

Thanks,
Gabriele

> Signed-off-by: Nam Cao <namcao@xxxxxxxxxxxxx>
> ---
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Ben Segall <bsegall@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> ---
>  include/trace/events/sched.h | 8 ++++++++
>  kernel/sched/rt.c            | 4 ++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/include/trace/events/sched.h
> b/include/trace/events/sched.h
> index c08893bde255..c38f12f7f903 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -898,6 +898,14 @@ DECLARE_TRACE(sched_set_need_resched,
>  	TP_PROTO(struct task_struct *tsk, int cpu, int tif),
>  	TP_ARGS(tsk, cpu, tif));
>  
> +DECLARE_TRACE(enqueue_task_rt,
> +	TP_PROTO(int cpu, struct task_struct *task),
> +	TP_ARGS(cpu, task));
> +
> +DECLARE_TRACE(dequeue_task_rt,
> +	TP_PROTO(int cpu, struct task_struct *task),
> +	TP_ARGS(cpu, task));
> +
>  #endif /* _TRACE_SCHED_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index e40422c37033..f4d3f5e7fbec 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1480,6 +1480,8 @@ enqueue_task_rt(struct rq *rq, struct
> task_struct *p, int flags)
>  {
>  	struct sched_rt_entity *rt_se = &p->rt;
>  
> +	trace_enqueue_task_rt_tp(rq->cpu, p);
> +
>  	if (flags & ENQUEUE_WAKEUP)
>  		rt_se->timeout = 0;
>  
> @@ -1501,6 +1503,8 @@ static bool dequeue_task_rt(struct rq *rq,
> struct task_struct *p, int flags)
>  
>  	dequeue_pushable_task(rq, p);
>  
> +	trace_dequeue_task_rt_tp(rq->cpu, p);
> +
>  	return true;
>  }
>