sched/fair: Optimize enqueue_task_fair()

enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is
throttled which means that se can't be NULL in such case and we can move
the label after the if (!se) statement. Futhermore, the latter can be
removed because se is always NULL when reaching this point.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/20200513135502.4672-1-vincent.guittot@linaro.org

kernel/sched/fair.c

@@ -5512,9 +5512,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
                        list_add_leaf_cfs_rq(cfs_rq);
 	}
 
-enqueue_throttle:
-	if (!se) {
+	/* At this point se is NULL and we are at root level*/
 	add_nr_running(rq, 1);
+
 	/*
 	 * Since new tasks are assigned an initial util_avg equal to
 	 * half of the spare capacity of their CPU, tiny tasks have the
@@ -5532,8 +5532,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	if (flags & ENQUEUE_WAKEUP)
 		update_overutilized_status(rq);
 
-	}
-
+enqueue_throttle:
 	if (cfs_bandwidth_used()) {
 		/*
 		 * When bandwidth control is enabled; the cfs_rq_throttled()