releases/4.14.60/tcp-add-one-more-quick-ack-after-after-ecn-events.patch

   1 From foo@baz Wed Aug  1 08:19:32 CEST 2018
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Wed, 27 Jun 2018 08:47:21 -0700
   4 Subject: tcp: add one more quick ack after after ECN events
   5
   6 From: Eric Dumazet <edumazet@google.com>
   7
   8 [ Upstream commit 15ecbe94a45ef88491ca459b26efdd02f91edb6d ]
   9
  10 Larry Brakmo proposal ( https://patchwork.ozlabs.org/patch/935233/
  11 tcp: force cwnd at least 2 in tcp_cwnd_reduction) made us rethink
  12 about our recent patch removing ~16 quick acks after ECN events.
  13
  14 tcp_enter_quickack_mode(sk, 1) makes sure one immediate ack is sent,
  15 but in the case the sender cwnd was lowered to 1, we do not want
  16 to have a delayed ack for the next packet we will receive.
  17
  18 Fixes: 522040ea5fdd ("tcp: do not aggressively quick ack after ECN events")
  19 Signed-off-by: Eric Dumazet <edumazet@google.com>
  20 Reported-by: Neal Cardwell <ncardwell@google.com>
  21 Cc: Lawrence Brakmo <brakmo@fb.com>
  22 Acked-by: Neal Cardwell <ncardwell@google.com>
  23 Signed-off-by: David S. Miller <davem@davemloft.net>
  24 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  25 ---
  26  net/ipv4/tcp_input.c |    4 ++--
  27  1 file changed, 2 insertions(+), 2 deletions(-)
  28
  29 --- a/net/ipv4/tcp_input.c
  30 +++ b/net/ipv4/tcp_input.c
  31 @@ -261,7 +261,7 @@ static void __tcp_ecn_check_ce(struct so
  32                  * it is probably a retransmit.
  33                  */
  34                 if (tp->ecn_flags & TCP_ECN_SEEN)
  35 -                       tcp_enter_quickack_mode(sk, 1);
  36 +                       tcp_enter_quickack_mode(sk, 2);
  37                 break;
  38         case INET_ECN_CE:
  39                 if (tcp_ca_needs_ecn(sk))
  40 @@ -269,7 +269,7 @@ static void __tcp_ecn_check_ce(struct so
  41
  42                 if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
  43                         /* Better not delay acks, sender can have a very low cwnd */
  44 -                       tcp_enter_quickack_mode(sk, 1);
  45 +                       tcp_enter_quickack_mode(sk, 2);
  46                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
  47                 }
  48                 tp->ecn_flags |= TCP_ECN_SEEN;