From 74c181d528bd8b5989f424a489262d0742ca31ae Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Mon, 12 Aug 2013 16:41:25 -0700 Subject: [PATCH] tcp: reset reordering est. selectively on timeout On timeout the TCP sender unconditionally resets the estimated degree of network reordering (tp->reordering). The idea behind this is that the estimate is too large to trigger fast recovery (e.g., due to a IP path change). But for example if the sender only had 2 packets outstanding, then a timeout doesn't tell much about reordering. A sender that learns about reordering on big writes and loses packets on small writes will end up falsely retransmitting again and again, especially when reordering is more likely on big writes. Therefore the sender should only suspect that tp->reordering is too high if it could have gone into fast recovery with the (lower) default estimate. Signed-off-by: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index b61274b666f6..e965cc7b87ff 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1877,8 +1877,13 @@ void tcp_enter_loss(struct sock *sk, int how) } tcp_verify_left_out(tp); - tp->reordering = min_t(unsigned int, tp->reordering, - sysctl_tcp_reordering); + /* Timeout in disordered state after receiving substantial DUPACKs + * suggests that the degree of reordering is over-estimated. + */ + if (icsk->icsk_ca_state <= TCP_CA_Disorder && + tp->sacked_out >= sysctl_tcp_reordering) + tp->reordering = min_t(unsigned int, tp->reordering, + sysctl_tcp_reordering); tcp_set_ca_state(sk, TCP_CA_Loss); tp->high_seq = tp->snd_nxt; TCP_ECN_queue_cwr(tp); -- 2.30.2