linux-kernel - [PATCH v2 6/6] sched: warn for high latency with TIF_NEED_RESCHED

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Message-Id: <20241106201758.428310-7-ankur.a.arora@oracle.com>
Date: Wed,  6 Nov 2024 12:17:58 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, tglx@...utronix.de, paulmck@...nel.org,
        mingo@...nel.org, bigeasy@...utronix.de, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        vschneid@...hat.com, frederic@...nel.org, ankur.a.arora@...cle.com,
        efault@....de, sshegde@...ux.ibm.com, boris.ostrovsky@...cle.com,
        Ingo Molnar <mingo@...hat.com>
Subject: [PATCH v2 6/6] sched: warn for high latency with TIF_NEED_RESCHED_LAZY

Add support for warning if the TIF_NEED_RESCHED_LAZY bit is set
without rescheduling for more than the latency_warn_ms period.

Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Ziljstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 kernel/sched/core.c  | 3 ++-
 kernel/sched/debug.c | 7 +++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5c47d70f4204..077ea42a17f1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5579,7 +5579,8 @@ static u64 cpu_resched_latency(struct rq *rq)
 	if (sysctl_resched_latency_warn_once && warned_once)
 		return 0;
 
-	if (!need_resched() || !latency_warn_ms)
+	if ((!need_resched() && !tif_test_bit(TIF_NEED_RESCHED_LAZY)) ||
+	    !latency_warn_ms)
 		return 0;
 
 	if (system_state == SYSTEM_BOOTING)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index a48b2a701ec2..6c1a5305a1b3 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1293,9 +1293,12 @@ void proc_sched_set_task(struct task_struct *p)
 void resched_latency_warn(int cpu, u64 latency)
 {
 	static DEFINE_RATELIMIT_STATE(latency_check_ratelimit, 60 * 60 * HZ, 1);
+	char *nr;
+
+	nr = tif_need_resched() ? "need_resched" : "need_resched_lazy";
 
 	WARN(__ratelimit(&latency_check_ratelimit),
-	     "sched: CPU %d need_resched set for > %llu ns (%d ticks) "
+	     "sched: CPU %d %s set for > %llu ns (%d ticks) "
 	     "without schedule\n",
-	     cpu, latency, cpu_rq(cpu)->ticks_without_resched);
+	     cpu, nr, latency, cpu_rq(cpu)->ticks_without_resched);
 }
-- 
2.43.5