sched: remove redundant hierarchy walk in check_preempt_wakeup

Impact: micro-optimization

Under group scheduling we traverse up until we are at common siblings
to make the wakeup comparison on.

At this point however, they should have the same parent so continuing
to check up the tree is redundant.

Signed-off-by: Paul Turner <pjt@google.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <alpine.DEB.1.00.0904081520320.30317@kitami.corp.google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_fair.c

@@ -1487,17 +1487,10 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int sync)
 
 	find_matching_se(&se, &pse);
 
-	while (se) {
-		BUG_ON(!pse);
+	BUG_ON(!pse);
 
-		if (wakeup_preempt_entity(se, pse) == 1) {
-			resched_task(curr);
-			break;
-		}
-
-		se = parent_entity(se);
-		pse = parent_entity(pse);
-	}
+	if (wakeup_preempt_entity(se, pse) == 1)
+		resched_task(curr);
 }
 
 static struct task_struct *pick_next_task_fair(struct rq *rq)