Re: [PATCH v3 12/17] sched: Adapt sched tracepoints for RV task model

On Wed, Jul 16, 2025 at 03:40:13PM +0200, Gabriele Monaco wrote:

On Wed, 2025-07-16 at 14:38 +0200, Peter Zijlstra wrote:

quoted

quoted

@@ -6786,6 +6793,7 @@ static void __sched notrace __schedule(int

sched_mode)
 		rq = context_switch(rq, prev, next, &rf);
 	} else {
 		rq_unpin_lock(rq, &rf);
+		trace_sched_switch_vain_tp(preempt, prev,
prev_state);
 		__balance_callbacks(rq);
 		raw_spin_rq_unlock_irq(rq);
 	}

Hurmph... don't you already have this covered by:
trace_sched_exit_tp() ?

Specifically, the only case where is_switch := false, is this case.

Mostly, it may work in some cases, but sched_exit happens with
interrupt enabled while all types of switches (including the vain ones)
must occur with interrupt disabled.

Some assumptions don't stand without this tracepoint, but I guess I
could adapt monitors to live without this if you believe it's not worth
adding a new tracepoint there.

I'm not sure I understand the importance of IRQ state when describing
task transitions.

You know both:

 - schedule() invocations for any one task are in-order;
 - schedule() invocations for any one CPU are in-order.