From 0ff8136eeca5fb038fdef3d8342838785df28685 Mon Sep 17 00:00:00 2001 From: Neal Cardwell Date: Sun, 7 Jan 2024 21:11:26 -0300 Subject: [PATCH 11/19] net-tcp: add fast_ack_mode=1: skip rwin check in tcp_fast_ack_mode__tcp_ack_snd_check() Add logic for an experimental TCP connection behavior, enabled with tp->fast_ack_mode = 1, which disables checking the receive window before sending an ack in __tcp_ack_snd_check(). If this behavior is enabled, the data receiver sends an ACK if the amount of data is > RCV.MSS. Change-Id: Iaa0a0fd7108221f883137a79d5bfa724f1b096d4 Signed-off-by: Alexandre Frade --- include/linux/tcp.h | 3 ++- net/ipv4/tcp.c | 1 + net/ipv4/tcp_cong.c | 1 + net/ipv4/tcp_input.c | 5 +++-- 4 files changed, 7 insertions(+), 3 deletions(-) --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -369,7 +369,8 @@ struct tcp_sock { u8 compressed_ack; u8 dup_ack_counter:2, tlp_retrans:1, /* TLP is a retransmission */ - unused:5; + fast_ack_mode:2, /* which fast ack mode ? */ + unused:3; u8 thin_lto : 1,/* Use linear timeouts for thin streams */ fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */ fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */ --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3397,6 +3397,7 @@ int tcp_disconnect(struct sock *sk, int tp->rx_opt.dsack = 0; tp->rx_opt.num_sacks = 0; tp->rcv_ooopack = 0; + tp->fast_ack_mode = 0; /* Clean up fastopen related fields */ --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -237,6 +237,7 @@ void tcp_init_congestion_control(struct struct inet_connection_sock *icsk = inet_csk(sk); tcp_sk(sk)->prior_ssthresh = 0; + tcp_sk(sk)->fast_ack_mode = 0; if (icsk->icsk_ca_ops->init) icsk->icsk_ca_ops->init(sk); if (tcp_ca_needs_ecn(sk)) --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5793,13 +5793,14 @@ static void __tcp_ack_snd_check(struct s /* More than one full frame received... */ if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss && + (tp->fast_ack_mode == 1 || /* ... and right edge of window advances far enough. * (tcp_recvmsg() will send ACK otherwise). * If application uses SO_RCVLOWAT, we want send ack now if * we have not received enough bytes to satisfy the condition. */ - (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat || - __tcp_select_window(sk) >= tp->rcv_wnd)) || + (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat || + __tcp_select_window(sk) >= tp->rcv_wnd))) || /* We ACK each frame or... */ tcp_in_quickack_mode(sk) || /* Protocol state mandates a one-time immediate ACK */