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

@@ -5512,28 +5512,27 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
                        list_add_leaf_cfs_rq(cfs_rq);
 	}
 
-enqueue_throttle:
-	if (!se) {
-		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
-		 * ability to cross the overutilized threshold, which will
-		 * result in the load balancer ruining all the task placement
-		 * done by EAS. As a way to mitigate that effect, do not account
-		 * for the first enqueue operation of new tasks during the
-		 * overutilized flag detection.
-		 *
-		 * A better way of solving this problem would be to wait for
-		 * the PELT signals of tasks to converge before taking them
-		 * into account, but that is not straightforward to implement,
-		 * and the following generally works well enough in practice.
-		 */
-		if (flags & ENQUEUE_WAKEUP)
-			update_overutilized_status(rq);
+	/* 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
+	 * ability to cross the overutilized threshold, which will
+	 * result in the load balancer ruining all the task placement
+	 * done by EAS. As a way to mitigate that effect, do not account
+	 * for the first enqueue operation of new tasks during the
+	 * overutilized flag detection.
+	 *
+	 * A better way of solving this problem would be to wait for
+	 * the PELT signals of tasks to converge before taking them
+	 * into account, but that is not straightforward to implement,
+	 * and the following generally works well enough in practice.
+	 */
+	if (flags & ENQUEUE_WAKEUP)
+		update_overutilized_status(rq);
 
+enqueue_throttle:
 	if (cfs_bandwidth_used()) {
 		/*
 		 * When bandwidth control is enabled; the cfs_rq_throttled()