[PATCH] sched: activate SCHED BATCH expired

To increase the strength of SCHED_BATCH as a scheduling hint we can
activate batch tasks on the expired array since by definition they are
latency insensitive tasks.
Signed-off-by: Con Kolivas <kernel@kolivas.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/sched.h

@@ -484,6 +484,7 @@ struct signal_struct {
 #define MAX_PRIO		(MAX_RT_PRIO + 40)
 
 #define rt_task(p)		(unlikely((p)->prio < MAX_RT_PRIO))
+#define batch_task(p)		(unlikely((p)->policy == SCHED_BATCH))
 
 /*
  * Some day this will be a full-fledged user tracking system..

kernel/sched.c

@@ -667,9 +667,13 @@ static int effective_prio(task_t *p)
 /*
  * __activate_task - move a task to the runqueue.
  */
-static inline void __activate_task(task_t *p, runqueue_t *rq)
+static void __activate_task(task_t *p, runqueue_t *rq)
 {
-	enqueue_task(p, rq->active);
+	prio_array_t *target = rq->active;
+
+	if (batch_task(p))
+		target = rq->expired;
+	enqueue_task(p, target);
 	rq->nr_running++;
 }
 
@@ -688,7 +692,7 @@ static int recalc_task_prio(task_t *p, unsigned long long now)
 	unsigned long long __sleep_time = now - p->timestamp;
 	unsigned long sleep_time;
 
-	if (unlikely(p->policy == SCHED_BATCH))
+	if (batch_task(p))
 		sleep_time = 0;
 	else {
 		if (__sleep_time > NS_MAX_SLEEP_AVG)