sched: RT-balance, add new methods to sched_class

Dmitry Adamushko found that the current implementation of the RT
balancing code left out changes to the sched_setscheduler and
rt_mutex_setprio.

This patch addresses this issue by adding methods to the schedule classes
to handle being switched out of (switched_from) and being switched into
(switched_to) a sched_class. Also a method for changing of priorities
is also added (prio_changed).

This patch also removes some duplicate logic between rt_mutex_setprio and
sched_setscheduler.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 89 insertions, 0 deletions

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index a5a45104603a..57fa3d96847b 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -779,7 +779,92 @@ static void leave_domain_rt(struct rq *rq)
         if (rq->rt.overloaded)
                 rt_clear_overload(rq);
 }
+
+/*
+ * When switch from the rt queue, we bring ourselves to a position
+ * that we might want to pull RT tasks from other runqueues.
+ */
+static void switched_from_rt(struct rq *rq, struct task_struct *p,
+                           int running)
+{
+        /*
+         * If there are other RT tasks then we will reschedule
+         * and the scheduling of the other RT tasks will handle
+         * the balancing. But if we are the last RT task
+         * we may need to handle the pulling of RT tasks
+         * now.
+         */
+        if (!rq->rt.rt_nr_running)
+                pull_rt_task(rq);
+}
+#endif /* CONFIG_SMP */
+
+/*
+ * When switching a task to RT, we may overload the runqueue
+ * with RT tasks. In this case we try to push them off to
+ * other runqueues.
+ */
+static void switched_to_rt(struct rq *rq, struct task_struct *p,
+                           int running)
+{
+        int check_resched = 1;
+
+        /*
+         * If we are already running, then there's nothing
+         * that needs to be done. But if we are not running
+         * we may need to preempt the current running task.
+         * If that current running task is also an RT task
+         * then see if we can move to another run queue.
+         */
+        if (!running) {
+#ifdef CONFIG_SMP
+                if (rq->rt.overloaded && push_rt_task(rq) &&
+                    /* Don't resched if we changed runqueues */
+                    rq != task_rq(p))
+                        check_resched = 0;
+#endif /* CONFIG_SMP */
+                if (check_resched && p->prio < rq->curr->prio)
+                        resched_task(rq->curr);
+        }
+}
+
+/*
+ * Priority of the task has changed. This may cause
+ * us to initiate a push or pull.
+ */
+static void prio_changed_rt(struct rq *rq, struct task_struct *p,
+                            int oldprio, int running)
+{
+        if (running) {
+#ifdef CONFIG_SMP
+                /*
+                 * If our priority decreases while running, we
+                 * may need to pull tasks to this runqueue.
+                 */
+                if (oldprio < p->prio)
+                        pull_rt_task(rq);
+                /*
+                 * If there's a higher priority task waiting to run
+                 * then reschedule.
+                 */
+                if (p->prio > rq->rt.highest_prio)
+                        resched_task(p);
+#else
+                /* For UP simply resched on drop of prio */
+                if (oldprio < p->prio)
+                        resched_task(p);
 #endif /* CONFIG_SMP */
+        } else {
+                /*
+                 * This task is not running, but if it is
+                 * greater than the current running task
+                 * then reschedule.
+                 */
+                if (p->prio < rq->curr->prio)
+                        resched_task(rq->curr);
+        }
+}
+
 
 static void task_tick_rt(struct rq *rq, struct task_struct *p)
 {
@@ -837,8 +922,12 @@ const struct sched_class rt_sched_class = {
         .pre_schedule           = pre_schedule_rt,
         .post_schedule          = post_schedule_rt,
         .task_wake_up           = task_wake_up_rt,
+        .switched_from          = switched_from_rt,
 #endif
 
         .set_curr_task          = set_curr_task_rt,
         .task_tick              = task_tick_rt,
+
+        .prio_changed           = prio_changed_rt,
+        .switched_to            = switched_to_rt,
 };