[PATCH] sched: consider migration thread with smp nice

[Con Kolivas <kernel@kolivas.org>]

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This patch improves throughput with the smp nice balancing code. Many thanks 
to Martin Bligh for the usage of his regression testing bed to confirm the 
effectiveness of various patches.

Con
---



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The intermittent scheduling of the migration thread at ultra high priority
makes the smp nice handling see that runqueue as being heavily loaded. The
migration thread itself actually handles the balancing so its influence on
priority balancing should be ignored.

Signed-off-by: Con Kolivas <kernel@kolivas.org>

Index: linux-2.6.12-mm1/kernel/sched.c
===================================================================
--- linux-2.6.12-mm1.orig/kernel/sched.c	2005-06-26 17:59:10.000000000 +1000
+++ linux-2.6.12-mm1/kernel/sched.c	2005-06-26 18:02:01.000000000 +1000
@@ -669,6 +669,31 @@ static inline void dec_prio_bias(runqueu
 {
 	rq->prio_bias -= MAX_PRIO - prio;
 }
+
+static inline void inc_nr_running(task_t *p, runqueue_t *rq)
+{
+	rq->nr_running++;
+	if (rt_task(p)) {
+		if (p != rq->migration_thread)
+			/*
+			 * The migration thread does the actual balancing. Do
+			 * not bias by its priority as the ultra high priority
+			 * will skew balancing adversely.
+			 */
+			inc_prio_bias(rq, p->prio);
+	} else
+		inc_prio_bias(rq, p->static_prio);
+}
+
+static inline void dec_nr_running(task_t *p, runqueue_t *rq)
+{
+	rq->nr_running--;
+	if (rt_task(p)) {
+		if (p != rq->migration_thread)
+			dec_prio_bias(rq, p->prio);
+	} else
+		dec_prio_bias(rq, p->static_prio);
+}
 #else
 static inline void inc_prio_bias(runqueue_t *rq, int prio)
 {
@@ -677,25 +702,17 @@ static inline void inc_prio_bias(runqueu
 static inline void dec_prio_bias(runqueue_t *rq, int prio)
 {
 }
-#endif
 
 static inline void inc_nr_running(task_t *p, runqueue_t *rq)
 {
 	rq->nr_running++;
-	if (rt_task(p))
-		inc_prio_bias(rq, p->prio);
-	else
-		inc_prio_bias(rq, p->static_prio);
 }
 
 static inline void dec_nr_running(task_t *p, runqueue_t *rq)
 {
 	rq->nr_running--;
-	if (rt_task(p))
-		dec_prio_bias(rq, p->prio);
-	else
-		dec_prio_bias(rq, p->static_prio);
 }
+#endif
 
 /*
  * __activate_task - move a task to the runqueue.

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