1 files changed, 69 insertions, 1 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e6c714b9b211..fcb35ae15619 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -58,7 +58,17 @@ const_debug unsigned int sysctl_sched_features =
 #include "features.h"
 	0;
 #undef SCHED_FEAT
-#endif
+
+/*
+ * Print a warning if need_resched is set for the given duration (if
+ * LATENCY_WARN is enabled).
+ *
+ * If sysctl_resched_latency_warn_once is set, only one warning will be shown
+ * per boot.
+ */
+__read_mostly int sysctl_resched_latency_warn_ms = 100;
+__read_mostly int sysctl_resched_latency_warn_once = 1;
+#endif /* CONFIG_SCHED_DEBUG */
 
 /*
  * Number of tasks to iterate in a single balance run.
@@ -4527,6 +4537,55 @@ unsigned long long task_sched_runtime(struct task_struct *p)
 	return ns;
 }
 
+#ifdef CONFIG_SCHED_DEBUG
+static u64 cpu_resched_latency(struct rq *rq)
+{
+	int latency_warn_ms = READ_ONCE(sysctl_resched_latency_warn_ms);
+	u64 resched_latency, now = rq_clock(rq);
+	static bool warned_once;
+
+	if (sysctl_resched_latency_warn_once && warned_once)
+		return 0;
+
+	if (!need_resched() || !latency_warn_ms)
+		return 0;
+
+	if (system_state == SYSTEM_BOOTING)
+		return 0;
+
+	if (!rq->last_seen_need_resched_ns) {
+		rq->last_seen_need_resched_ns = now;
+		rq->ticks_without_resched = 0;
+		return 0;
+	}
+
+	rq->ticks_without_resched++;
+	resched_latency = now - rq->last_seen_need_resched_ns;
+	if (resched_latency <= latency_warn_ms * NSEC_PER_MSEC)
+		return 0;
+
+	warned_once = true;
+
+	return resched_latency;
+}
+
+static int __init setup_resched_latency_warn_ms(char *str)
+{
+	long val;
+
+	if ((kstrtol(str, 0, &val))) {
+		pr_warn("Unable to set resched_latency_warn_ms\n");
+		return 1;
+	}
+
+	sysctl_resched_latency_warn_ms = val;
+	return 1;
+}
+__setup("resched_latency_warn_ms=", setup_resched_latency_warn_ms);
+#else
+static inline u64 cpu_resched_latency(struct rq *rq) { return 0; }
+#endif /* CONFIG_SCHED_DEBUG */
+
 /*
  * This function gets called by the timer code, with HZ frequency.
  * We call it with interrupts disabled.
@@ -4538,6 +4597,7 @@ void scheduler_tick(void)
 	struct task_struct *curr = rq->curr;
 	struct rq_flags rf;
 	unsigned long thermal_pressure;
+	u64 resched_latency;
 
 	arch_scale_freq_tick();
 	sched_clock_tick();
@@ -4548,10 +4608,15 @@ void scheduler_tick(void)
 	thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
 	update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
 	curr->sched_class->task_tick(rq, curr, 0);
+	if (sched_feat(LATENCY_WARN))
+		resched_latency = cpu_resched_latency(rq);
 	calc_global_load_tick(rq);
 
 	rq_unlock(rq, &rf);
 
+	if (sched_feat(LATENCY_WARN) && resched_latency)
+		resched_latency_warn(cpu, resched_latency);
+
 	perf_event_task_tick();
 
 #ifdef CONFIG_SMP
@@ -5046,6 +5111,9 @@ static void __sched notrace __schedule(bool preempt)
 	next = pick_next_task(rq, prev, &rf);
 	clear_tsk_need_resched(prev);
 	clear_preempt_need_resched();
+#ifdef CONFIG_SCHED_DEBUG
+	rq->last_seen_need_resched_ns = 0;
+#endif
 
 	if (likely(prev != next)) {
 		rq->nr_switches++;