sched: push RT tasks from overloaded CPUs

This patch adds pushing of overloaded RT tasks from a runqueue that is
having tasks (most likely RT tasks) added to the run queue.

TODO: We don't cover the case of waking of new RT tasks (yet).
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -1710,6 +1710,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
 
 out_running:
 	p->state = TASK_RUNNING;
+	wakeup_balance_rt(rq, p);
 out:
 	task_rq_unlock(rq, &flags);
 

kernel/sched_rt.c

@@ -558,6 +558,15 @@ static void schedule_tail_balance_rt(struct rq *rq)
 	}
 }
 
+
+static void wakeup_balance_rt(struct rq *rq, struct task_struct *p)
+{
+	if (unlikely(rt_task(p)) &&
+	    !task_running(rq, p) &&
+	    (p->prio >= rq->curr->prio))
+		push_rt_tasks(rq);
+}
+
 /*
  * Load-balancing iterator. Note: while the runqueue stays locked
  * during the whole iteration, the current task might be
@@ -665,6 +674,7 @@ move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 #else /* CONFIG_SMP */
 # define schedule_tail_balance_rt(rq)	do { } while (0)
 # define schedule_balance_rt(rq, prev)	do { } while (0)
+# define wakeup_balance_rt(rq, p)	do { } while (0)
 #endif /* CONFIG_SMP */
 
 static void task_tick_rt(struct rq *rq, struct task_struct *p)