sched, rt: Convert switched_{from, to}_rt() / prio_changed_rt() to balance callbacks

Remove the direct {push,pull} balancing operations from
switched_{from,to}_rt() / prio_changed_rt() 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/20150611124742.766832367@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index c702b48de9f0f1f1905929b1c19a820c59778f83..460f85888b74d52453e62025a337a3d9b60aabe7 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -354,16 +354,23 @@ static inline int has_pushable_tasks(struct rq *rq)
        return !plist_head_empty(&rq->rt.pushable_tasks);
 }
 
-static DEFINE_PER_CPU(struct callback_head, rt_balance_head);
+static DEFINE_PER_CPU(struct callback_head, rt_push_head);
+static DEFINE_PER_CPU(struct callback_head, rt_pull_head);
 
 static void push_rt_tasks(struct rq *);
+static void pull_rt_task(struct rq *);
 
 static inline void queue_push_tasks(struct rq *rq)
 {
        if (!has_pushable_tasks(rq))
                return;
 
-       queue_balance_callback(rq, &per_cpu(rt_balance_head, rq->cpu), push_rt_tasks);
+       queue_balance_callback(rq, &per_cpu(rt_push_head, rq->cpu), push_rt_tasks);
+}
+
+static inline void queue_pull_task(struct rq *rq)
+{
+       queue_balance_callback(rq, &per_cpu(rt_pull_head, rq->cpu), pull_rt_task);
 }
 
 static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
@@ -2139,7 +2146,7 @@ static void switched_from_rt(struct rq *rq, struct task_struct *p)
        if (!task_on_rq_queued(p) || rq->rt.rt_nr_running)
                return;
 
-       pull_rt_task(rq);
+       queue_pull_task(rq);
 }
 
 void __init init_sched_rt_class(void)
@@ -2160,8 +2167,6 @@ void __init init_sched_rt_class(void)
  */
 static void switched_to_rt(struct rq *rq, struct task_struct *p)
 {
-       int check_resched = 1;
-
        /*
         * If we are already running, then there's nothing
         * that needs to be done. But if we are not running
@@ -2171,13 +2176,12 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
         */
        if (task_on_rq_queued(p) && rq->curr != p) {
 #ifdef CONFIG_SMP
-               if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
-                   /* Don't resched if we changed runqueues */
-                   push_rt_task(rq) && rq != task_rq(p))
-                       check_resched = 0;
-#endif /* CONFIG_SMP */
-               if (check_resched && p->prio < rq->curr->prio)
+               if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
+                       queue_push_tasks(rq);
+#else
+               if (p->prio < rq->curr->prio)
                        resched_curr(rq);
+#endif /* CONFIG_SMP */
        }
 }
 
@@ -2198,14 +2202,13 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
                 * may need to pull tasks to this runqueue.
                 */
                if (oldprio < p->prio)
-                       pull_rt_task(rq);
+                       queue_pull_task(rq);
+
                /*
                 * If there's a higher priority task waiting to run
-                * then reschedule. Note, the above pull_rt_task
-                * can release the rq lock and p could migrate.
-                * Only reschedule if p is still on the same runqueue.
+                * then reschedule.
                 */
-               if (p->prio > rq->rt.highest_prio.curr && rq->curr == p)
+               if (p->prio > rq->rt.highest_prio.curr)
                        resched_curr(rq);
 #else
                /* For UP simply resched on drop of prio */