sched, dl: Convert switched_{from, to}_dl() / prio_changed_dl() to balance callbacks

commit 9916e214 upstream.

Remove the direct {push,pull} balancing operations from
switched_{from,to}_dl() / prio_changed_dl() and use the balance
callback queue.

Again, err on the side of too many reschedules; since too few is a
hard bug while too many is just annoying.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: ktkhai@parallels.com
Cc: rostedt@goodmis.org
Cc: juri.lelli@gmail.com
Cc: pang.xunlei@linaro.org
Cc: oleg@redhat.com
Cc: wanpeng.li@linux.intel.com
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20150611124742.968262663@infradead.orgSigned-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/sched/deadline.c

@@ -210,16 +210,23 @@ static inline int has_pushable_dl_tasks(struct rq *rq)
 
 static int push_dl_task(struct rq *rq);
 
-static DEFINE_PER_CPU(struct callback_head, dl_balance_head);
+static DEFINE_PER_CPU(struct callback_head, dl_push_head);
+static DEFINE_PER_CPU(struct callback_head, dl_pull_head);
 
 static void push_dl_tasks(struct rq *);
+static void pull_dl_task(struct rq *);
 
 static inline void queue_push_tasks(struct rq *rq)
 {
 	if (!has_pushable_dl_tasks(rq))
 		return;
 
-	queue_balance_callback(rq, &per_cpu(dl_balance_head, rq->cpu), push_dl_tasks);
+	queue_balance_callback(rq, &per_cpu(dl_push_head, rq->cpu), push_dl_tasks);
+}
+
+static inline void queue_pull_task(struct rq *rq)
+{
+	queue_balance_callback(rq, &per_cpu(dl_pull_head, rq->cpu), pull_dl_task);
 }
 
 #else
@@ -247,6 +254,10 @@ void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
 static inline void queue_push_tasks(struct rq *rq)
 {
 }
+
+static inline void queue_pull_task(struct rq *rq)
+{
+}
 #endif /* CONFIG_SMP */
 
 static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags);
@@ -1541,7 +1552,7 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
 	 * from an overloaded cpu, if any.
 	 */
 	if (!rq->dl.dl_nr_running)
-		pull_dl_task(rq);
+		queue_pull_task(rq);
 #endif
 }
 
@@ -1551,8 +1562,6 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
  */
 static void switched_to_dl(struct rq *rq, struct task_struct *p)
 {
-	int check_resched = 1;
-
 	/*
 	 * If p is throttled, don't consider the possibility
 	 * of preempting rq->curr, the check will be done right
@@ -1563,12 +1572,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 
 	if (p->on_rq || rq->curr != p) {
 #ifdef CONFIG_SMP
-		if (rq->dl.overloaded && push_dl_task(rq) && rq != task_rq(p))
-			/* Only reschedule if pushing failed */
-			check_resched = 0;
-#endif /* CONFIG_SMP */
-		if (check_resched && task_has_dl_policy(rq->curr))
+		if (rq->dl.overloaded)
+			queue_push_tasks(rq);
+#else
+		if (task_has_dl_policy(rq->curr))
 			check_preempt_curr_dl(rq, p, 0);
+#endif /* CONFIG_SMP */
 	}
 }
 
@@ -1588,15 +1597,14 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
 		 * or lowering its prio, so...
 		 */
 		if (!rq->dl.overloaded)
-			pull_dl_task(rq);
+			queue_pull_task(rq);
 
 		/*
 		 * If we now have a earlier deadline task than p,
 		 * then reschedule, provided p is still on this
 		 * runqueue.
 		 */
-		if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
-		    rq->curr == p)
+		if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline))
 			resched_task(p);
 #else
 		/*