diff options
| author | Neal Cardwell <ncardwell@google.com> | 2011-11-16 08:58:04 +0000 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2011-11-27 18:54:09 -0500 |
| commit | f698204bd0bfdc645642e271da117b56b795aee0 (patch) | |
| tree | a08c3714c3f1e0e523db799d0455b9e9b17fa8ab /net | |
| parent | e95ae2f2cf10f7bf27b492aa6188f3cd745de162 (diff) | |
| download | linux-f698204bd0bfdc645642e271da117b56b795aee0.tar.bz2 | |
tcp: allow undo from reordered DSACKs
Previously, SACK-enabled connections hung around in TCP_CA_Disorder
state while snd_una==high_seq, just waiting to accumulate DSACKs and
hopefully undo a cwnd reduction. This could and did lead to the
following unfortunate scenario: if some incoming ACKs advance snd_una
beyond high_seq then we were setting undo_marker to 0 and moving to
TCP_CA_Open, so if (due to reordering in the ACK return path) we
shortly thereafter received a DSACK then we were no longer able to
undo the cwnd reduction.
The change: Simplify the congestion avoidance state machine by
removing the behavior where SACK-enabled connections hung around in
the TCP_CA_Disorder state just waiting for DSACKs. Instead, when
snd_una advances to high_seq or beyond we typically move to
TCP_CA_Open immediately and allow an undo in either TCP_CA_Open or
TCP_CA_Disorder if we later receive enough DSACKs.
Other patches in this series will provide other changes that are
necessary to fully fix this problem.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
| -rw-r--r-- | net/ipv4/tcp_input.c | 15 |
1 files changed, 2 insertions, 13 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 751d39060fb8..a4efdd7cf5a1 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2858,7 +2858,7 @@ static void tcp_try_keep_open(struct sock *sk) struct tcp_sock *tp = tcp_sk(sk); int state = TCP_CA_Open; - if (tcp_left_out(tp) || tcp_any_retrans_done(sk) || tp->undo_marker) + if (tcp_left_out(tp) || tcp_any_retrans_done(sk)) state = TCP_CA_Disorder; if (inet_csk(sk)->icsk_ca_state != state) { @@ -3066,17 +3066,6 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, } break; - case TCP_CA_Disorder: - tcp_try_undo_dsack(sk); - if (!tp->undo_marker || - /* For SACK case do not Open to allow to undo - * catching for all duplicate ACKs. */ - tcp_is_reno(tp) || tp->snd_una != tp->high_seq) { - tp->undo_marker = 0; - tcp_set_ca_state(sk, TCP_CA_Open); - } - break; - case TCP_CA_Recovery: if (tcp_is_reno(tp)) tcp_reset_reno_sack(tp); @@ -3117,7 +3106,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, tcp_add_reno_sack(sk); } - if (icsk->icsk_ca_state == TCP_CA_Disorder) + if (icsk->icsk_ca_state <= TCP_CA_Disorder) tcp_try_undo_dsack(sk); if (!tcp_time_to_recover(sk)) { |