path: root/net/tipc
diff options
authorJon Maloy <jon.maloy@ericsson.com>2019-12-10 00:52:44 +0100
committerDavid S. Miller <davem@davemloft.net>2019-12-10 17:31:15 -0800
commit02288248b051ae9a9438278148f44bdfb0a4068b (patch)
treea9cc3f1ee1249054a96403f83b0c552dd5f8094a /net/tipc
parentppp: Adjust indentation into ppp_async_input (diff)
tipc: eliminate gap indicator from ACK messages
When we increase the link send window we sometimes observe the following scenario: 1) A packet #N arrives out of order far ahead of a sequence of older packets which are still under way. The packet is added to the deferred queue. 2) The missing packets arrive in sequence, and for each 16th of them an ACK is sent back to the receiver, as it should be. 3) When building those ACK messages, it is checked if there is a gap between the link's 'rcv_nxt' and the first packet in the deferred queue. This is always the case until packet number #N-1 arrives, and a 'gap' indicator is added, effectively turning them into NACK messages. 4) When those NACKs arrive at the sender, all the requested retransmissions are done, since it is a first-time request. This sometimes leads to a huge amount of redundant retransmissions, causing a drop in max throughput. This problem gets worse when we in a later commit introduce variable window congestion control, since it drops the link back to 'fast recovery' much more often than necessary. We now fix this by not sending any 'gap' indicator in regular ACK messages. We already have a mechanism for sending explicit NACKs in place, and this is sufficient to keep up the packet flow. Acked-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>
Diffstat (limited to 'net/tipc')
1 files changed, 9 insertions, 5 deletions
diff --git a/net/tipc/link.c b/net/tipc/link.c
index 24d4d10756d3..6d864461f83c 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -1521,7 +1521,8 @@ static int tipc_link_build_nack_msg(struct tipc_link *l,
struct sk_buff_head *xmitq)
u32 def_cnt = ++l->stats.deferred_recv;
- u32 defq_len = skb_queue_len(&l->deferdq);
+ struct sk_buff_head *dfq = &l->deferdq;
+ u32 defq_len = skb_queue_len(dfq);
int match1, match2;
if (link_is_bc_rcvlink(l)) {
@@ -1532,8 +1533,12 @@ static int tipc_link_build_nack_msg(struct tipc_link *l,
return 0;
- if (defq_len >= 3 && !((defq_len - 3) % 16))
- tipc_link_build_proto_msg(l, STATE_MSG, 0, 0, 0, 0, 0, xmitq);
+ if (defq_len >= 3 && !((defq_len - 3) % 16)) {
+ u16 rcvgap = buf_seqno(skb_peek(dfq)) - l->rcv_nxt;
+ tipc_link_build_proto_msg(l, STATE_MSG, 0, 0,
+ rcvgap, 0, 0, xmitq);
+ }
return 0;
@@ -1631,7 +1636,7 @@ static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
if (!tipc_link_is_up(l) && (mtyp == STATE_MSG))
- if (!skb_queue_empty(dfq))
+ if ((probe || probe_reply) && !skb_queue_empty(dfq))
rcvgap = buf_seqno(skb_peek(dfq)) - l->rcv_nxt;
skb = tipc_msg_create(LINK_PROTOCOL, mtyp, INT_H_SIZE,
@@ -2079,7 +2084,6 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
if (rcvgap || reply)
tipc_link_build_proto_msg(l, STATE_MSG, 0, reply,
rcvgap, 0, 0, xmitq);
rc |= tipc_link_advance_transmq(l, ack, gap, ga, xmitq);
/* If NACK, retransmit will now start at right position */