tcp: add one more quick ack after after ECN events

[ Upstream commit 15ecbe94a45ef88491ca459b26efdd02f91edb6d ]

Larry Brakmo proposal ( https://patchwork.ozlabs.org/patch/935233/
tcp: force cwnd at least 2 in tcp_cwnd_reduction) made us rethink
about our recent patch removing ~16 quick acks after ECN events.

tcp_enter_quickack_mode(sk, 1) makes sure one immediate ack is sent,
but in the case the sender cwnd was lowered to 1, we do not want
to have a delayed ack for the next packet we will receive.

Fixes: 522040ea5fdd ("tcp: do not aggressively quick ack after ECN events")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Neal Cardwell <ncardwell@google.com>
Cc: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index ee6602d..a9be8df 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -261,7 +261,7 @@ static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
                 * it is probably a retransmit.
                 */
                if (tp->ecn_flags & TCP_ECN_SEEN)
-                       tcp_enter_quickack_mode(sk, 1);
+                       tcp_enter_quickack_mode(sk, 2);
                break;
        case INET_ECN_CE:
                if (tcp_ca_needs_ecn(sk))
@@ -269,7 +269,7 @@ static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 
                if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
                        /* Better not delay acks, sender can have a very low cwnd */
-                       tcp_enter_quickack_mode(sk, 1);
+                       tcp_enter_quickack_mode(sk, 2);
                        tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
                }
                tp->ecn_flags |= TCP_ECN_SEEN;