[TCP]: Send ACKs each 2nd received segment. (1ef9696c) · Commits · 戴 / test

It does not affect either mss-sized connections (obviously) or connections controlled by Nagle (because there is only one small segment in flight). The idea is to record the fact that a small segment arrives on a connection, where one small segment has already been received and still not-ACKed. In this case ACK is forced after tcp_recvmsg() drains receive buffer. In other words, it is a "soft" each-2nd-segment ACK, which is enough to preserve ACK clock even when ABC is enabled. Signed-off-by:

Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/net/inet_connection_sock.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -147,7 +147,8 @@ extern struct sock inet_csk_clone(struct sock sk,
		enum inet_csk_ack_state_t {
		ICSK_ACK_SCHED = 1,
		ICSK_ACK_TIMER = 2,
		ICSK_ACK_PUSHED = 4
		ICSK_ACK_PUSHED = 4,
		ICSK_ACK_PUSHED2 = 8
		};

		extern void inet_csk_init_xmit_timers(struct sock *sk,

net/ipv4/tcp.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -955,8 +955,11 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied)
		* receive buffer and there was a small segment
		* in queue.
		*/
		(copied > 0 && (icsk->icsk_ack.pending & ICSK_ACK_PUSHED) &&
		!icsk->icsk_ack.pingpong && !atomic_read(&sk->sk_rmem_alloc)))
		(copied > 0 &&
		((icsk->icsk_ack.pending & ICSK_ACK_PUSHED2) \|\|
		((icsk->icsk_ack.pending & ICSK_ACK_PUSHED) &&
		!icsk->icsk_ack.pingpong)) &&
		!atomic_read(&sk->sk_rmem_alloc)))
		time_to_ack = 1;
		}

net/ipv4/tcp_input.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -156,6 +156,8 @@ static void tcp_measure_rcv_mss(struct sock *sk,
		return;
		}
		}
		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
		icsk->icsk_ack.pending \|= ICSK_ACK_PUSHED2;
		icsk->icsk_ack.pending \|= ICSK_ACK_PUSHED;
		}
		}

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