On Mon, May 21, 2018 at 3:08 PM, Eric Dumazet <eduma...@google.com> wrote:
> 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 <eduma...@google.com>
> ---
Acked-by: Yuchung Cheng <ych...@google.com>
Thanks for this patch. I am still wondering how much does the "funny
extension" help. but this patch definitely reduce the amount of
unnecessary immediate ACKs on ECN.
> net/ipv4/tcp_input.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index
> 2e970e9f4e09d966b703af2d14d521a4328eba7e..1191cac72109f2f7e2b688ddbc1d404151d274d6
> 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -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;
> --
> 2.17.0.441.gb46fe60e1d-goog
>
