linux-kernel - Re: [PATCH v2] sched/rt: Fix rt task's sched latency statistics error in sched_stat_wait trace

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Date: Sat, 23 Dec 2023 05:36:34 +0000
From: Junwen Wu <wudaemon@....com>
To: laoar.shao@...il.com
Cc: bristot@...hat.com,
	bsegall@...gle.com,
	dietmar.eggemann@....com,
	juri.lelli@...hat.com,
	linux-kernel@...r.kernel.org,
	mgorman@...e.de,
	mingo@...hat.com,
	peterz@...radead.org,
	rostedt@...dmis.org,
	vincent.guittot@...aro.org,
	vschneid@...hat.com,
	wudaemon@....com
Subject: Re: [PATCH v2] sched/rt: Fix rt task's sched latency statistics error in sched_stat_wait trace_point

>It seems DL has the same issue. Pls. also fix it in update_stats_dequeue_dl().
>And add the Fixes tag in the commit log:
>Fixes: 57a5c2dafca8 ("sched/rt: Support schedstats for RT sched class")
>Fixes: b5eb4a5f6521 ("sched/dl: Support schedstats for deadline sched class")

ok, the PATCH v3 below is ok?

Subject: [PATCH v3] sched/stats: Fix rt/dl task's sched latency statistics
 error in sched_stat_wait trace_point

When enable sched_stat_wait trace_point, some rt tasks sched latency so long, like this,
sched_stat_wait: comm=rcu_preempt pid=14 delay=4936139545261 [ns]
Rt task has low latency, it must have a bug. When rt task balance off source cpu,
dequeue operation not update the sched_statistics, so follow update_stats_wait_end_fair
update method, so do dl tasks.

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 | 8 +++++++-
 kernel/sched/rt.c       | 7 +++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index b28114478b82..29223163ee22 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1558,10 +1558,16 @@ 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..6a2600213991 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1360,12 +1360,19 @@ 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;

--
Best regards