sched: track highest prio task queued

This patch adds accounting to each runqueue to keep track of the
highest prio task queued on the run queue. We only care about
RT tasks, so if the run queue does not contain any active RT tasks
its priority will be considered MAX_RT_PRIO.

This information will be used for later patches.

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

1 files changed, 18 insertions, 0 deletions

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index e3d2ca8832af..136c2857a049 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -30,6 +30,10 @@ static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
 {
 	WARN_ON(!rt_task(p));
 	rq->rt.rt_nr_running++;
+#ifdef CONFIG_SMP
+	if (p->prio < rq->rt.highest_prio)
+		rq->rt.highest_prio = p->prio;
+#endif /* CONFIG_SMP */
 }
 
 static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
@@ -37,6 +41,20 @@ static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
 	WARN_ON(!rt_task(p));
 	WARN_ON(!rq->rt.rt_nr_running);
 	rq->rt.rt_nr_running--;
+#ifdef CONFIG_SMP
+	if (rq->rt.rt_nr_running) {
+		struct rt_prio_array *array;
+
+		WARN_ON(p->prio < rq->rt.highest_prio);
+		if (p->prio == rq->rt.highest_prio) {
+			/* recalculate */
+			array = &rq->rt.active;
+			rq->rt.highest_prio =
+				sched_find_first_bit(array->bitmap);
+		} /* otherwise leave rq->highest prio alone */
+	} else
+		rq->rt.highest_prio = MAX_RT_PRIO;
+#endif /* CONFIG_SMP */
 }
 
 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)