[PATCH] sched/rt: Check if rt_se has neighbour in requeue_task_rt()

[Kirill Tkhai <tkhai@yandex.ru>]

1)requeue_task_rt: check if entity's next and prev are not the same element.
This guarantees entity is queued and it is not the only in the prio list.
Return 1 if at least one rt_se from the stack was really requeued.

2)Remove on_rt_rq check from requeue_rt_entity() because it is useless now.
Furthermore, it doesn't handle single rt_se case.

3)Make pretty task_tick_rt() more pretty.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/rt.c |   49 +++++++++++++++++++++++--------------------------
 1 files changed, 23 insertions(+), 26 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 01970c8..3213503 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1135,29 +1135,37 @@ static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
  * Put task to the head or the end of the run list without the overhead of
  * dequeue followed by enqueue.
  */
-static void
+static inline void
 requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se, int head)
 {
-	if (on_rt_rq(rt_se)) {
-		struct rt_prio_array *array = &rt_rq->active;
-		struct list_head *queue = array->queue + rt_se_prio(rt_se);
+	struct rt_prio_array *array = &rt_rq->active;
+	struct list_head *queue = array->queue + rt_se_prio(rt_se);
 
-		if (head)
-			list_move(&rt_se->run_list, queue);
-		else
-			list_move_tail(&rt_se->run_list, queue);
-	}
+	if (head)
+		list_move(&rt_se->run_list, queue);
+	else
+		list_move_tail(&rt_se->run_list, queue);
 }
 
-static void requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
+static int requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
 {
 	struct sched_rt_entity *rt_se = &p->rt;
-	struct rt_rq *rt_rq;
+	int requeued = 0;
 
 	for_each_sched_rt_entity(rt_se) {
-		rt_rq = rt_rq_of_se(rt_se);
-		requeue_rt_entity(rt_rq, rt_se, head);
+		/*
+		 * Requeue to the head or tail of prio queue if
+		 * rt_se is queued and it is not the only element
+		 */
+		if (rt_se->run_list.prev != rt_se->run_list.next) {
+			struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
+
+			requeue_rt_entity(rt_rq, rt_se, head);
+			requeued = 1;
+		}
 	}
+
+	return requeued;
 }
 
 static void yield_task_rt(struct rq *rq)
@@ -1912,8 +1920,6 @@ static void watchdog(struct rq *rq, struct task_struct *p)
 
 static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
 {
-	struct sched_rt_entity *rt_se = &p->rt;
-
 	update_curr_rt(rq);
 
 	watchdog(rq, p);
@@ -1930,17 +1936,8 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
 
 	p->rt.time_slice = sched_rr_timeslice;
 
-	/*
-	 * Requeue to the end of queue if we (and all of our ancestors) are the
-	 * only element on the queue
-	 */
-	for_each_sched_rt_entity(rt_se) {
-		if (rt_se->run_list.prev != rt_se->run_list.next) {
-			requeue_task_rt(rq, p, 0);
-			set_tsk_need_resched(p);
-			return;
-		}
-	}
+	if (requeue_task_rt(rq, p, 0))
+		set_tsk_need_resched(p);
 }
 
 static void set_curr_task_rt(struct rq *rq)