sched: default to more agressive yield for SCHED_BATCH tasks

do more agressive yield for SCHED_BATCH tuned tasks: they are all
about throughput anyway. This allows a gentler migration path for
any apps that relied on stronger yield.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 37bb265..c33f0ce 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -799,8 +799,9 @@
  */
 static void yield_task_fair(struct rq *rq)
 {
-	struct cfs_rq *cfs_rq = task_cfs_rq(rq->curr);
-	struct sched_entity *rightmost, *se = &rq->curr->se;
+	struct task_struct *curr = rq->curr;
+	struct cfs_rq *cfs_rq = task_cfs_rq(curr);
+	struct sched_entity *rightmost, *se = &curr->se;
 
 	/*
 	 * Are we the only task in the tree?
@@ -808,7 +809,7 @@
 	if (unlikely(cfs_rq->nr_running == 1))
 		return;
 
-	if (likely(!sysctl_sched_compat_yield)) {
+	if (likely(!sysctl_sched_compat_yield) && curr->policy != SCHED_BATCH) {
 		__update_rq_clock(rq);
 		/*
 		 * Update run-time statistics of the 'current'.