path: root/net/ipv4/tcp_input.c
diff options
authorYuchung Cheng <ycheng@google.com>2019-04-29 15:46:16 -0700
committerDavid S. Miller <davem@davemloft.net>2019-05-01 11:47:54 -0400
commit336c39a0315139103712d04b9bfaf0215df23b8e (patch)
tree65339ecab2ce54cdbad17a91fa20c8b835cf7d82 /net/ipv4/tcp_input.c
parenttcp: better SYNACK sent timestamp (diff)
tcp: undo init congestion window on false SYNACK timeout
Linux implements RFC6298 and use an initial congestion window of 1 upon establishing the connection if the SYNACK packet is retransmitted 2 or more times. In cellular networks SYNACK timeouts are often spurious if the wireless radio was dormant or idle. Also some network path is longer than the default SYNACK timeout. In both cases falsely starting with a minimal cwnd are detrimental to performance. This patch avoids doing so when the final ACK's TCP timestamp indicates the original SYNACK was delivered. It remembers the original SYNACK timestamp when SYNACK timeout has occurred and re-uses the function to detect spurious SYN timeout conveniently. Note that a server may receives multiple SYNs from and immediately retransmits SYNACKs without any SYNACK timeout. This often happens on when the client SYNs have timed out due to wireless delay above. In this case since the server will still use the default initial congestion (e.g. 10) because tp->undo_marker is reset in tcp_init_metrics(). This is an intentional design because packets are not lost but delayed. This patch only covers regular TCP passive open. Fast Open is supported in the next patch. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to '')
1 files changed, 2 insertions, 0 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 30c6a42b1f5b..53b4c5a3113b 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6101,6 +6101,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
} else {
+ tcp_try_undo_spurious_syn(sk);
+ tp->retrans_stamp = 0;
tp->copied_seq = tp->rcv_nxt;