[patch 4/8] RT overloaded runqueues accounting

[Steven Rostedt]

This patch adds an RT overload accounting system. When a runqueue has
more than one RT task queued, it is marked as overloaded. That is that it
is a candidate to have RT tasks pulled from it.

Along with the rt_overload counter (number of overloaded runqueues) a
bit mask of overloaded runqueues with RT tasks is set.

Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/sched_rt.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

Index: linux-test.git/kernel/sched_rt.c
===================================================================
--- linux-test.git.orig/kernel/sched_rt.c	2007-10-19 12:34:46.000000000 -0400
+++ linux-test.git/kernel/sched_rt.c	2007-10-19 12:35:58.000000000 -0400
@@ -25,10 +25,23 @@ static void update_curr_rt(struct rq *rq
 	curr->se.exec_start = rq->clock;
 }
 
+#ifdef CONFIG_SMP
+static __cacheline_aligned_in_smp atomic_t rt_overload;
+static cpumask_t rto_cpumask;
+#endif /* CONFIG_SMP*/
+
 static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
 {
 	if (rt_task(p))
 		rq->rt_nr_running++;
+#ifdef CONFIG_SMP
+	if (rq->rt_nr_running == 2) {
+		cpu_set(rq->cpu, rto_cpumask);
+		/* Make sure this cpu is visible on rt_overloads */
+		smp_wmb();
+		atomic_inc(&rt_overload);
+	}
+#endif
 }
 
 static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
@@ -37,6 +50,12 @@ static inline void dec_rt_tasks(struct t
 		WARN_ON(!rq->rt_nr_running);
 		rq->rt_nr_running--;
 	}
+#ifdef CONFIG_SMP
+	if (rq->rt_nr_running == 1) {
+		atomic_dec(&rt_overload);
+		cpu_clear(rq->cpu, rto_cpumask);
+	}
+#endif
 }
 
 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)

-- 
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