Commit 15ecbe94 authored Jun 27, 2018 by Eric Dumazet Committed by David S. Miller Jun 28, 2018

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: 522040ea ("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>

parent 8e75887d

net/ipv4/tcp_input.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -265,7 +265,7 @@ 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))
		@@ -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)) {
		/* 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;

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