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tcp: add one more quick ack after after ECN events 

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: 522040ea5f ("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>
This commit is contained in:
Eric Dumazet 2018-06-27 08:47:21 -07:00 committed by David S. Miller
parent 8e75887d32
commit 15ecbe94a4
1 changed files with 2 additions and 2 deletions
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4
net/ipv4/tcp_input.c
View File

@ -265,7 +265,7 @@ static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
* it is probably a retransmit. * it is probably a retransmit.
*/ */
if (tp->ecn_flags & TCP_ECN_SEEN) if (tp->ecn_flags & TCP_ECN_SEEN)
tcp_enter_quickack_mode(sk, 1); tcp_enter_quickack_mode(sk, 2);
break; break;
case INET_ECN_CE: case INET_ECN_CE:
if (tcp_ca_needs_ecn(sk)) if (tcp_ca_needs_ecn(sk))
@ -273,7 +273,7 @@ static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) { if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
/* Better not delay acks, sender can have a very low cwnd */ /* 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_DEMAND_CWR;
} }
tp->ecn_flags |= TCP_ECN_SEEN; tp->ecn_flags |= TCP_ECN_SEEN;