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tcp: do not aggressively quick ack after ECN events 

[ Upstream commit 522040ea5f ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
pull/10/head
Eric Dumazet 2018-05-21 15:08:57 -07:00 committed by Greg Kroah-Hartman
parent 1c005489fa
commit fd31083cbe
1 changed files with 2 additions and 2 deletions
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4
net/ipv4/tcp_input.c
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@ -259,7 +259,7 @@ 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))
@ -267,7 +267,7 @@ 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;