linux-kernel - [PATCH v3 4/5] sched: Add task enqueue/dequeue trace points

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Message-Id: <918fe0f29a94e49db05c4f63a8a210dda9b90925.1754900299.git.namcao@linutronix.de>
Date: Mon, 11 Aug 2025 10:40:52 +0200
From: Nam Cao <namcao@...utronix.de>
To: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Gabriele Monaco <gmonaco@...hat.com>,
	linux-trace-kernel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Nam Cao <namcao@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>
Subject: [PATCH v3 4/5] sched: Add task enqueue/dequeue trace points

Add trace points into enqueue_task() and dequeue_task(). They are useful to
implement RV monitor which validates RT scheduling.

Signed-off-by: Nam Cao <namcao@...utronix.de>
---
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>
---
v3: fix up build issue on !SMP
v2: Move the tracepoints to cover all task enqueue/dequeue, not just RT
---
 include/trace/events/sched.h | 13 +++++++++++++
 kernel/sched/core.c          |  8 +++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 7b2645b50e78..696d22af5a98 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -896,6 +896,19 @@ DECLARE_TRACE(sched_set_need_resched,
 	TP_PROTO(struct task_struct *tsk, int cpu, int tif),
 	TP_ARGS(tsk, cpu, tif));
 
+/*
+ * 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-ace2-67b5e672fdee@amd.com/
+ */
+DECLARE_TRACE(enqueue_task,
+	TP_PROTO(int cpu, struct task_struct *task),
+	TP_ARGS(cpu, task));
+
+DECLARE_TRACE(dequeue_task,
+	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/core.c b/kernel/sched/core.c
index be00629f0ba4..6367799aa023 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2077,6 +2077,8 @@ unsigned long get_wchan(struct task_struct *p)
 
 void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 {
+	trace_enqueue_task_tp(cpu_of(rq), p);
+
 	if (!(flags & ENQUEUE_NOCLOCK))
 		update_rq_clock(rq);
 
@@ -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(cpu_of(rq), p);
+		return true;
+	}
+	return false;
 }
 
 void activate_task(struct rq *rq, struct task_struct *p, int flags)
-- 
2.39.5