linux-kernel - [PATCH v4] sched/stats: Fix rt/dl task's sched latency statistics error in sched_stat_wait trace

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Date: Wed, 10 Jan 2024 13:30:38 +0000
From: Junwen Wu <wudaemon@....com>
To: bristot@...hat.com,
	mingo@...hat.com,
	laoar.shao@...il.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com
Cc: mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org,
	Junwen Wu <wudaemon@....com>
Subject: [PATCH v4] sched/stats: Fix rt/dl task's sched latency statistics error in sched_stat_wait trace_point

The sched_stat_wait tracepoint is showing unreasonably long
latencies for real-time tasks. For example:

sched_stat_wait: comm=rcu_preempt pid=14 delay=4936139545261 [ns]

This error happens when the rt task balances off the source CPU because
the dequeue operation is not updating the sched_statistics. So, follow
update_stats_wait_end_fair() and update the stats. Do the same for
SCHED_DEADLINE.

Fixes: 57a5c2dafca8 ("sched/rt: Support schedstats for RT sched class")
Fixes: b5eb4a5f6521 ("sched/dl: Support schedstats for deadline sched class")
Signed-off-by: Junwen Wu <wudaemon@....com>
---
 kernel/sched/deadline.c | 5 ++++-
 kernel/sched/rt.c       | 4 ++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index b28114478b82..4a9aad291fb9 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1558,10 +1558,13 @@ update_stats_dequeue_dl(struct dl_rq *dl_rq, struct sched_dl_entity *dl_se,
 			int flags)
 {
 	struct task_struct *p = dl_task_of(dl_se);
+	struct rq *rq = rq_of_dl_rq(dl_rq);
 
 	if (!schedstat_enabled())
 		return;
-
+	/*  Mark the end of the wait period if dequeueing a waiting task.*/
+	if (p && (p != rq->curr))
+		 update_stats_wait_end_dl(dl_rq, dl_se);
 	if ((flags & DEQUEUE_SLEEP)) {
 		unsigned int state;
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 6aaf0a3d6081..5cb3a54d6b13 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1360,12 +1360,16 @@ update_stats_dequeue_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se,
 			int flags)
 {
 	struct task_struct *p = NULL;
+	struct rq *rq = rq_of_rt_se(rt_se);
 
 	if (!schedstat_enabled())
 		return;
 
 	if (rt_entity_is_task(rt_se))
 		p = rt_task_of(rt_se);
+	/* Mark the end of the wait period if dequeueing a waiting task. */
+	if (p && (p != rq->curr))
+		update_stats_wait_end_rt(rt_rq, rt_se);
 
 	if ((flags & DEQUEUE_SLEEP) && p) {
 		unsigned int state;
-- 
2.34.1