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tcp: mandate a one-time immediate ACK

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Add a new flag to indicate a one-time immediate ACK. This flag is
occasionaly set under specific TCP protocol states in addition to
the more common quickack mechanism for interactive application.

In several cases in the TCP code we want to force an immediate ACK
but do not want to call tcp_enter_quickack_mode() because we do
not want to forget the icsk_ack.pingpong or icsk_ack.ato state.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng 2018-08-09 09:38:09 -07:00 committed by David S. Miller
parent 8a8a894ebb
commit 466466dc6c
2 changed files with 5 additions and 2 deletions
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3
include/net/inet_connection_sock.h
View File

@ -167,7 +167,8 @@ enum inet_csk_ack_state_t {
ICSK_ACK_SCHED = 1,
ICSK_ACK_TIMER = 2,
ICSK_ACK_PUSHED = 4,
ICSK_ACK_PUSHED2 = 8
ICSK_ACK_PUSHED2 = 8,
ICSK_ACK_NOW = 16 /* Send the next ACK immediately (once) */
};
void inet_csk_init_xmit_timers(struct sock *sk,

4
net/ipv4/tcp_input.c
View File

@ -5179,7 +5179,9 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
(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)) {
tcp_in_quickack_mode(sk) ||
/* Protocol state mandates a one-time immediate ACK */
inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
send_now:
tcp_send_ack(sk);
return;