linux-kernel - [PATCH] sched/rt: Print curr when RT throttling activated

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Date:   Thu, 3 Dec 2020 15:51:29 +0800
From:   Xianting Tian <tian.xianting@....com>
To:     <mingo@...hat.com>, <peterz@...radead.org>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <dietmar.eggemann@....com>, <rostedt@...dmis.org>,
        <bsegall@...gle.com>, <mgorman@...e.de>
CC:     <linux-kernel@...r.kernel.org>,
        Xianting Tian <tian.xianting@....com>
Subject: [PATCH] sched/rt: Print curr when RT throttling activated

We may meet the issue, that one RT thread occupied the cpu by 950ms/1s,
The RT thread maybe is a business thread or other unknown thread.

Currently, it only outputs the print "sched: RT throttling activated"
when RT throttling happen. It is hard to know what is the RT thread,
For further analysis, we need add more prints.

This patch is to print current RT task when RT throttling activated,
It help us to know what is the RT thread in the first time.

Signed-off-by: Xianting Tian <tian.xianting@....com>
---
 kernel/sched/rt.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index f215eea6a..8913f38cb 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -946,7 +946,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, struct task_struct *curr)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -970,7 +970,8 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 		 */
 		if (likely(rt_b->rt_runtime)) {
 			rt_rq->rt_throttled = 1;
-			printk_deferred_once("sched: RT throttling activated\n");
+			printk_deferred_once("sched: RT throttling activated (curr: pid %d, comm %s)\n",
+						curr->pid, curr->comm);
 		} else {
 			/*
 			 * In case we did anyway, make it go away,
@@ -1026,7 +1027,7 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			if (sched_rt_runtime_exceeded(rt_rq))
+			if (sched_rt_runtime_exceeded(rt_rq, curr))
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
 		}
-- 
2.17.1