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Subject[PATCH v3 04/17] RT overloaded runqueues accounting
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.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
kernel/sched_rt.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
Index: linux-compile.git/kernel/sched_rt.c
===================================================================
--- linux-compile.git.orig/kernel/sched_rt.c 2007-11-16 21:56:29.000000000 -0500
+++ linux-compile.git/kernel/sched_rt.c 2007-11-16 22:12:07.000000000 -0500
@@ -3,6 +3,38 @@
* policies)
*/

+#ifdef CONFIG_SMP
+static cpumask_t rt_overload_mask;
+static atomic_t rto_count;
+static inline int rt_overloaded(void)
+{
+ return atomic_read(&rto_count);
+}
+static inline cpumask_t *rt_overload(void)
+{
+ return &rt_overload_mask;
+}
+static inline void rt_set_overload(struct rq *rq)
+{
+ cpu_set(rq->cpu, rt_overload_mask);
+ /*
+ * Make sure the mask is visible before we set
+ * the overload count. That is checked to determine
+ * if we should look at the mask. It would be a shame
+ * if we looked at the mask, but the mask was not
+ * updated yet.
+ */
+ wmb();
+ atomic_inc(&rto_count);
+}
+static inline void rt_clear_overload(struct rq *rq)
+{
+ /* the order here really doesn't matter */
+ atomic_dec(&rto_count);
+ cpu_clear(rq->cpu, rt_overload_mask);
+}
+#endif /* CONFIG_SMP */
+
/*
* Update the current task's runtime statistics. Skip current tasks that
* are not in our scheduling class.
@@ -32,6 +64,8 @@ static inline void inc_rt_tasks(struct t
#ifdef CONFIG_SMP
if (p->prio < rq->rt.highest_prio)
rq->rt.highest_prio = p->prio;
+ if (rq->rt.rt_nr_running > 1)
+ rt_set_overload(rq);
#endif /* CONFIG_SMP */
}

@@ -53,6 +87,8 @@ static inline void dec_rt_tasks(struct t
} /* otherwise leave rq->highest prio alone */
} else
rq->rt.highest_prio = MAX_RT_PRIO;
+ if (rq->rt.rt_nr_running < 2)
+ rt_clear_overload(rq);
#endif /* CONFIG_SMP */
}

--
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