Commit 522040ea authored May 21, 2018 by Eric Dumazet Committed by David S. Miller May 22, 2018

tcp: do not aggressively quick ack after ECN events



ECN signals currently forces TCP to enter quickack mode for
up to 16 (TCP_MAX_QUICKACKS) following incoming packets.

We believe this is not needed, and only sending one immediate ack
for the current packet should be enough.

This should reduce the extra load noticed in DCTCP environments,
after congestion events.

This is part 2 of our effort to reduce pure ACK packets.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 9a9c9b51

net/ipv4/tcp_input.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -263,7 +263,7 @@ static void __tcp_ecn_check_ce(struct tcp_sock tp, const struct sk_buff skb)
		* it is probably a retransmit.
		*/
		if (tp->ecn_flags & TCP_ECN_SEEN)
		tcp_enter_quickack_mode((struct sock *)tp, TCP_MAX_QUICKACKS);
		tcp_enter_quickack_mode((struct sock *)tp, 1);
		break;
		case INET_ECN_CE:
		if (tcp_ca_needs_ecn((struct sock *)tp))
		@@ -271,7 +271,7 @@ static void __tcp_ecn_check_ce(struct tcp_sock tp, 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((struct sock *)tp, TCP_MAX_QUICKACKS);
		tcp_enter_quickack_mode((struct sock *)tp, 1);
		tp->ecn_flags \|= TCP_ECN_DEMAND_CWR;
		}
		tp->ecn_flags \|= TCP_ECN_SEEN;