On Wed, Aug 06, 2025 at 10:01:20AM +0200, Nam Cao wrote:
> +/*
> + * The two trace points below may not work as expected for fair tasks due
> + * to delayed dequeue. See:
> + * https://lore.kernel.org/lkml/179674c6-f82a-4718-ace2-67b5e672f...@amd.com/
> + */
> +DECLARE_TRACE(dequeue_task,
> + TP_PROTO(int cpu, struct task_struct *task),
> + TP_ARGS(cpu, task));
> +
> @@ -2119,7 +2121,11 @@ inline bool dequeue_task(struct rq *rq, struct
> task_struct *p, int flags)
> * and mark the task ->sched_delayed.
> */
> uclamp_rq_dec(rq, p);
> - return p->sched_class->dequeue_task(rq, p, flags);
> + if (p->sched_class->dequeue_task(rq, p, flags)) {
> + trace_dequeue_task_tp(rq->cpu, p);
> + return true;
> + }
> + return false;
> }
Hurmpff.. that's not very nice.
How about something like:
dequeue_task():
...
ret = p->sched_class->dequeue_task(rq, p, flags);
if (trace_dequeue_task_p_enabled() && !(flags & DEQUEUE_SLEEP))
__trace_dequeue_task_tp(rq->cpu, p);
return ret;
__block_task():
trace_dequeue_task_tp(rq->cpu, p);
...
Specifically, only DEQUEUE_SLEEP is allowed to fail, and DEQUEUE_SLEEP
will eventually cause __block_task() to be called, either directly, or
delayed.
