【解説】Linux 6.11以降で発生しているリグレッションについて

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 99c80abdbaaac1..aba23b08e52dc4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5765,6 +5765,7 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
 	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
 	struct sched_entity *se;
 	long task_delta, idle_task_delta, dequeue = 1;
+	long rq_h_nr_running = rq->cfs.h_nr_running;
 
 	raw_spin_lock(&cfs_b->lock);
 	/* This will start the period timer if necessary */

@@ -5837,6 +5838,9 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
 	sub_nr_running(rq, task_delta);
 
 done:
+	/* Stop the fair server if throttling resulted in no runnable tasks */
+	if (rq_h_nr_running && !rq->cfs.h_nr_running)
+		dl_server_stop(&rq->fair_server);
 	/*
 	 * Note: distribution will already see us throttled via the
 	 * throttled-list.  rq->lock protects completion.

@@ -5854,6 +5858,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
 	struct sched_entity *se;
 	long task_delta, idle_task_delta;
+	long rq_h_nr_running = rq->cfs.h_nr_running;
 
 	se = cfs_rq->tg->se[cpu_of(rq)];
 
@@ -5929,6 +5934,10 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 unthrottle_throttle:
 	assert_list_leaf_cfs_rq(rq);
 
+	/* Start the fair server if un-throttling resulted in new runnable tasks */
+	if (!rq_h_nr_running && rq->cfs.h_nr_running)
+		dl_server_start(&rq->fair_server);
+
 	/* Determine whether we need to wake up potentially idle CPU: */
 	if (rq->curr == rq->idle && rq->cfs.nr_running)
 		resched_curr(rq);

@@ -6759,6 +6768,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	 */
 	util_est_enqueue(&rq->cfs, p);
 
+	if (!throttled_hierarchy(task_cfs_rq(p)) && !rq->cfs.h_nr_running)
+		dl_server_start(&rq->fair_server);
+
 	/*
 	 * If in_iowait is set, the code below may not trigger any cpufreq
 	 * utilization updates, so do it here explicitly with the IOWAIT flag

@@ -6903,6 +6915,9 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 		rq->next_balance = jiffies;
 
 dequeue_throttle:
+	if (!throttled_hierarchy(task_cfs_rq(p)) && !rq->cfs.h_nr_running)
+		dl_server_stop(&rq->fair_server);
+
 	util_est_update(&rq->cfs, p, task_sleep);
 	hrtick_update(rq);
 }
@@ -8602,6 +8617,25 @@ static struct task_struct *__pick_next_task_fair(struct rq *rq)
 	return pick_next_task_fair(rq, NULL, NULL);
 }