tipc: transfer broadcast nacks in link state messages

When we send broadcasts in clusters of more 70-80 nodes, we sometimes
see the broadcast link resetting because of an excessive number of
retransmissions. This is caused by a combination of two factors:

1) A 'NACK crunch", where loss of broadcast packets is discovered
   and NACK'ed by several nodes simultaneously, leading to multiple
   redundant broadcast retransmissions.

2) The fact that the NACKS as such also are sent as broadcast, leading
   to excessive load and packet loss on the transmitting switch/bridge.

This commit deals with the latter problem, by moving sending of
broadcast nacks from the dedicated BCAST_PROTOCOL/NACK message type
to regular unicast LINK_PROTOCOL/STATE messages. We allocate 10 unused
bits in word 8 of the said message for this purpose, and introduce a
new capability bit, TIPC_BCAST_STATE_NACK in order to keep the change
backwards compatible.

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

1 files changed, 5 insertions, 3 deletions

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index ae469b37d852..753f774cb46f 100644
--- a/net/tipc/bcast.c
+++ b/net/tipc/bcast.c
@@ -269,18 +269,19 @@ void tipc_bcast_ack_rcv(struct net *net, struct tipc_link *l, u32 acked)
  *
  * RCU is locked, no other locks set
  */
-void tipc_bcast_sync_rcv(struct net *net, struct tipc_link *l,
-                         struct tipc_msg *hdr)
+int tipc_bcast_sync_rcv(struct net *net, struct tipc_link *l,
+                        struct tipc_msg *hdr)
 {
         struct sk_buff_head *inputq = &tipc_bc_base(net)->inputq;
         struct sk_buff_head xmitq;
+        int rc = 0;
 
         __skb_queue_head_init(&xmitq);
 
         tipc_bcast_lock(net);
         if (msg_type(hdr) == STATE_MSG) {
                 tipc_link_bc_ack_rcv(l, msg_bcast_ack(hdr), &xmitq);
-                tipc_link_bc_sync_rcv(l, hdr, &xmitq);
+                rc = tipc_link_bc_sync_rcv(l, hdr, &xmitq);
         } else {
                 tipc_link_bc_init_rcv(l, hdr);
         }
@@ -291,6 +292,7 @@ void tipc_bcast_sync_rcv(struct net *net, struct tipc_link *l,
         /* Any socket wakeup messages ? */
         if (!skb_queue_empty(inputq))
                 tipc_sk_rcv(net, inputq);
+        return rc;
 }
 
 /* tipc_bcast_add_peer - add a peer node to broadcast link and bearer