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authorAllan Stephens <allan.stephens@windriver.com>2011-10-27 14:17:53 -0400
committerPaul Gortmaker <paul.gortmaker@windriver.com>2012-02-06 16:59:18 -0500
commit7a54d4a99dcbbfdf1d4550faa19b615091137953 (patch)
tree34b685bc29547373a43b0f3bd15cf54c07c01971 /net/tipc/node.c
parentb98158e3b36645305363a598d91c544fa31446f1 (diff)
tipc: Major redesign of broadcast link ACK/NACK algorithms
Completely redesigns broadcast link ACK and NACK mechanisms to prevent spurious retransmit requests in dual LAN networks, and to prevent the broadcast link from stalling due to the failure of a receiving node to acknowledge receiving a broadcast message or request its retransmission. Note: These changes only impact the timing of when ACK and NACK messages are sent, and not the basic broadcast link protocol itself, so inter- operability with nodes using the "classic" algorithms is maintained. The revised algorithms are as follows: 1) An explicit ACK message is still sent after receiving 16 in-sequence messages, and implicit ACK information continues to be carried in other unicast link message headers (including link state messages). However, the timing of explicit ACKs is now based on the receiving node's absolute network address rather than its relative network address to ensure that the failure of another node does not delay the ACK beyond its 16 message target. 2) A NACK message is now typically sent only when a message gap persists for two consecutive incoming link state messages; this ensures that a suspected gap is not confirmed until both LANs in a dual LAN network have had an opportunity to deliver the message, thereby preventing spurious NACKs. A NACK message can also be generated by the arrival of a single link state message, if the deferred queue is so big that the current message gap cannot be the result of "normal" mis-ordering due to the use of dual LANs (or one LAN using a bonded interface). Since link state messages typically arrive at different nodes at different times the problem of multiple nodes issuing identical NACKs simultaneously is inherently avoided. 3) Nodes continue to "peek" at NACK messages sent by other nodes. If another node requests retransmission of a message gap suspected (but not yet confirmed) by the peeking node, the peeking node forgets about the gap and does not generate a duplicate retransmit request. (If the peeking node subsequently fails to receive the lost message, later link state messages will cause it to rediscover and confirm the gap and send another NACK.) 4) Message gap "equality" is now determined by the start of the gap only. This is sufficient to deal with the most common cases of message loss, and eliminates the need for complex end of gap computations. 5) A peeking node no longer tries to determine whether it should send a complementary NACK, since the most common cases of message loss don't require it to be sent. Consequently, the node no longer examines the "broadcast tag" field of a NACK message when peeking. Signed-off-by: Allan Stephens <allan.stephens@windriver.com> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Diffstat (limited to 'net/tipc/node.c')
-rw-r--r--net/tipc/node.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/net/tipc/node.c b/net/tipc/node.c
index 9196f943b83..6d8bdfd95cd 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -339,12 +339,12 @@ static void node_lost_contact(struct tipc_node *n_ptr)
/* Flush broadcast link info associated with lost node */
if (n_ptr->bclink.supported) {
- n_ptr->bclink.gap_after = n_ptr->bclink.gap_to = 0;
while (n_ptr->bclink.deferred_head) {
struct sk_buff *buf = n_ptr->bclink.deferred_head;
n_ptr->bclink.deferred_head = buf->next;
buf_discard(buf);
}
+ n_ptr->bclink.deferred_size = 0;
if (n_ptr->bclink.defragm) {
buf_discard(n_ptr->bclink.defragm);
@@ -450,7 +450,7 @@ struct sk_buff *tipc_node_get_links(const void *req_tlv_area, int req_tlv_space)
read_lock_bh(&tipc_net_lock);
- /* Get space for all unicast links + multicast link */
+ /* Get space for all unicast links + broadcast link */
payload_size = TLV_SPACE(sizeof(link_info)) *
(atomic_read(&tipc_num_links) + 1);