tipc: simplify tipc_link_rcv() reception loop

Currently, all packets received in tipc_link_rcv() are unconditionally
added to the packet deferred queue, whereafter that queue is walked and
all its buffers evaluated for delivery. This is both non-optimal and
and makes the queue sorting function unnecessary complex.

This commit changes the loop so that an arrived packet is evaluated
first, and added to the deferred queue only when a sequence number gap
is discovered. A non-empty deferred queue is walked until it is empty
or until its head's sequence number doesn't fit.

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/link.c

@@ -1047,44 +1047,55 @@ static bool tipc_link_release_pkts(struct tipc_link *l, u16 acked)
 	return released;
 }
 
+/* tipc_link_build_ack_msg: prepare link acknowledge message for transmission
+ */
+void tipc_link_build_ack_msg(struct tipc_link *l, struct sk_buff_head *xmitq)
+{
+	l->rcv_unacked = 0;
+	l->stats.sent_acks++;
+	tipc_link_build_proto_msg(l, STATE_MSG, 0, 0, 0, 0, xmitq);
+}
+
+/* tipc_link_build_nack_msg: prepare link nack message for transmission
+ */
+static void tipc_link_build_nack_msg(struct tipc_link *l,
+				     struct sk_buff_head *xmitq)
+{
+	u32 def_cnt = ++l->stats.deferred_recv;
+
+	if ((skb_queue_len(&l->deferdq) == 1) || !(def_cnt % TIPC_NACK_INTV))
+		tipc_link_build_proto_msg(l, STATE_MSG, 0, 0, 0, 0, xmitq);
+}
+
 /* tipc_link_rcv - process TIPC packets/messages arriving from off-node
- * @link: the link that should handle the message
+ * @l: the link that should handle the message
  * @skb: TIPC packet
  * @xmitq: queue to place packets to be sent after this call
  */
 int tipc_link_rcv(struct tipc_link *l, struct sk_buff *skb,
 		  struct sk_buff_head *xmitq)
 {
-	struct sk_buff_head *arrvq = &l->deferdq;
+	struct sk_buff_head *defq = &l->deferdq;
 	struct tipc_msg *hdr;
 	u16 seqno, rcv_nxt;
 	int rc = 0;
 
-	if (unlikely(!__tipc_skb_queue_sorted(arrvq, skb))) {
-		if (!(skb_queue_len(arrvq) % TIPC_NACK_INTV))
-			tipc_link_build_proto_msg(l, STATE_MSG, 0,
-						  0, 0, 0, xmitq);
-		return rc;
-	}
-
-	while ((skb = skb_peek(arrvq))) {
+	do {
 		hdr = buf_msg(skb);
+		seqno = msg_seqno(hdr);
+		rcv_nxt = l->rcv_nxt;
 
 		/* Verify and update link state */
-		if (unlikely(msg_user(hdr) == LINK_PROTOCOL)) {
-			__skb_dequeue(arrvq);
-			rc = tipc_link_proto_rcv(l, skb, xmitq);
-			continue;
-		}
+		if (unlikely(msg_user(hdr) == LINK_PROTOCOL))
+			return tipc_link_proto_rcv(l, skb, xmitq);
 
 		if (unlikely(!link_is_up(l))) {
 			rc = tipc_link_fsm_evt(l, LINK_ESTABLISH_EVT);
-			if (!link_is_up(l)) {
-				kfree_skb(__skb_dequeue(arrvq));
-				goto exit;
-			}
+			if (!link_is_up(l))
+				goto drop;
 		}
 
+		/* Don't send probe at next timeout expiration */
 		l->silent_intv_cnt = 0;
 
 		/* Forward queues and wake up waiting users */
@@ -1095,37 +1106,36 @@ int tipc_link_rcv(struct tipc_link *l, struct sk_buff *skb,
 		}
 
 		/* Defer reception if there is a gap in the sequence */
-		seqno = msg_seqno(hdr);
-		rcv_nxt = l->rcv_nxt;
 		if (unlikely(less(rcv_nxt, seqno))) {
-			l->stats.deferred_recv++;
-			goto exit;
+			__tipc_skb_queue_sorted(defq, skb);
+			tipc_link_build_nack_msg(l, xmitq);
+			break;
 		}
 
-		__skb_dequeue(arrvq);
-
 		/* Drop if packet already received */
 		if (unlikely(more(rcv_nxt, seqno))) {
 			l->stats.duplicates++;
-			kfree_skb(skb);
-			goto exit;
+			goto drop;
 		}
 
 		/* Packet can be delivered */
 		l->rcv_nxt++;
 		l->stats.recv_info++;
-		if (unlikely(!tipc_data_input(l, skb, l->inputq)))
+
+		if (!tipc_data_input(l, skb, l->inputq))
 			rc = tipc_link_input(l, skb, l->inputq);
+		if (rc)
+			break;
 
 		/* Ack at regular intervals */
-		if (unlikely(++l->rcv_unacked >= TIPC_MIN_LINK_WIN)) {
-			l->rcv_unacked = 0;
-			l->stats.sent_acks++;
-			tipc_link_build_proto_msg(l, STATE_MSG,
-						  0, 0, 0, 0, xmitq);
-		}
-	}
-exit:
+		if (unlikely(++l->rcv_unacked >= TIPC_MIN_LINK_WIN))
+			tipc_link_build_ack_msg(l, xmitq);
+
+	} while ((skb = __skb_dequeue(defq)));
+
+	return rc;
+drop:
+	kfree_skb(skb);
 	return rc;
 }
 
@@ -1249,7 +1259,7 @@ static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
 }
 
 /* tipc_link_tnl_prepare(): prepare and return a list of tunnel packets
- * with contents of the link's tranmsit and backlog queues.
+ * with contents of the link's transmit and backlog queues.
  */
 void tipc_link_tnl_prepare(struct tipc_link *l, struct tipc_link *tnl,
 			   int mtyp, struct sk_buff_head *xmitq)