4.4-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
[ Upstream commit 522040ea5fdd1c33bbf75e1d7c7c0422b96a94ef ]
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 --- net/ipv4/tcp_input.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -237,7 +237,7 @@ static void __tcp_ecn_check_ce(struct tc * 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)) @@ -245,7 +245,7 @@ static void __tcp_ecn_check_ce(struct tc
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;