[patch 2/8] track highest prio queued on runqueue

[Steven Rostedt]

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 <rostedt@xxxxxxxxxxx>

---
 kernel/sched.c    |    7 +++++++
 kernel/sched_rt.c |   25 +++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

Index: linux-test.git/kernel/sched.c
===================================================================
--- linux-test.git.orig/kernel/sched.c	2007-10-19 12:33:09.000000000 -0400
+++ linux-test.git/kernel/sched.c	2007-10-19 12:34:32.000000000 -0400
@@ -324,6 +324,8 @@ struct rq {
 	int push_cpu;
 	/* cpu of this runqueue: */
 	int cpu;
+	/* highest queued rt task prio */
+	int highest_prio;
 
 	struct task_struct *migration_thread;
 	struct list_head migration_queue;
@@ -972,6 +974,8 @@ static void activate_task(struct rq *rq,
 
 	enqueue_task(rq, p, wakeup);
 	inc_nr_running(p, rq);
+
+	rq_prio_add_task(rq, p);
 }
 
 /*
@@ -984,6 +988,8 @@ static void deactivate_task(struct rq *r
 
 	dequeue_task(rq, p, sleep);
 	dec_nr_running(p, rq);
+
+	rq_prio_remove_task(rq, p);
 }
 
 /**
@@ -6619,6 +6625,7 @@ void __init sched_init(void)
 		rq->cpu = i;
 		rq->migration_thread = NULL;
 		INIT_LIST_HEAD(&rq->migration_queue);
+		rq->highest_prio = MAX_RT_PRIO;
 #endif
 		atomic_set(&rq->nr_iowait, 0);
 
Index: linux-test.git/kernel/sched_rt.c
===================================================================
--- linux-test.git.orig/kernel/sched_rt.c	2007-10-19 12:33:09.000000000 -0400
+++ linux-test.git/kernel/sched_rt.c	2007-10-19 12:33:23.000000000 -0400
@@ -110,6 +110,31 @@ static struct task_struct *pick_next_tas
 	return next;
 }
 
+#ifdef CONFIG_SMP
+static inline void rq_prio_add_task(struct rq *rq, struct task_struct *p)
+{
+	if (unlikely(rt_task(p)) && p->prio < rq->highest_prio)
+		rq->highest_prio = p->prio;
+}
+
+static inline void rq_prio_remove_task(struct rq *rq, struct task_struct *p)
+{
+	struct rt_prio_array *array;
+
+	if (unlikely(rt_task(p))) {
+		if (rq->rt_nr_running) {
+			if (p->prio >= rq->highest_prio) {
+				/* recalculate */
+				array = &rq->rt.active;
+				rq->highest_prio =
+					sched_find_first_bit(array->bitmap);
+			} /* otherwise leave rq->highest prio alone */
+		} else
+			rq->highest_prio = MAX_RT_PRIO;
+	}
+}
+#endif /* CONFIG_SMP */
+
 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
 {
 	update_curr_rt(rq);

-- 
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