tipc: optimize function tipc_node_timeout()

In single-link usage, the function tipc_node_timeout() still iterates
over the whole link array to handle each link. Given that the maximum
number of bearers are 3, there are 2 redundant iterations with lock
grab/release. Since this function is executing very frequently it makes
sense to optimize it.

This commit adds conditional checking to exit from the loop if the
known number of configured links has already been accessed.
Acked-by: NYing Xue <ying.xue@windriver.com>
Signed-off-by: NTung Nguyen <tung.q.nguyen@dektech.com.au>
Signed-off-by: NJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/tipc/node.c

@@ -551,21 +551,23 @@ static void tipc_node_timeout(struct timer_list *t)
 	struct tipc_node *n = from_timer(n, t, timer);
 	struct tipc_link_entry *le;
 	struct sk_buff_head xmitq;
+	int remains = n->link_cnt;
 	int bearer_id;
 	int rc = 0;
 
 	__skb_queue_head_init(&xmitq);
 
-	for (bearer_id = 0; bearer_id < MAX_BEARERS; bearer_id++) {
+	for (bearer_id = 0; remains && (bearer_id < MAX_BEARERS); bearer_id++) {
 		tipc_node_read_lock(n);
 		le = &n->links[bearer_id];
-		spin_lock_bh(&le->lock);
 		if (le->link) {
+			spin_lock_bh(&le->lock);
 			/* Link tolerance may change asynchronously: */
 			tipc_node_calculate_timer(n, le->link);
 			rc = tipc_link_timeout(le->link, &xmitq);
+			spin_unlock_bh(&le->lock);
+			remains--;
 		}
-		spin_unlock_bh(&le->lock);
 		tipc_node_read_unlock(n);
 		tipc_bearer_xmit(n->net, bearer_id, &xmitq, &le->maddr);
 		if (rc & TIPC_LINK_DOWN_EVT)