sched: minor fast-path overhead reduction

Greetings,

103638d added a bit of avoidable overhead to the fast-path.

Use sysctl_sched_min_granularity instead of sched_slice() to restrict buddy wakeups.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_fair.c

@@ -747,7 +747,7 @@ pick_next(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	struct rq *rq = rq_of(cfs_rq);
 	u64 pair_slice = rq->clock - cfs_rq->pair_start;
 
-	if (!cfs_rq->next || pair_slice > sched_slice(cfs_rq, cfs_rq->next)) {
+	if (!cfs_rq->next || pair_slice > sysctl_sched_min_granularity) {
 		cfs_rq->pair_start = rq->clock;
 		return se;
 	}