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[TCP]: Send ACKs each 2nd received segment.

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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>
This commit is contained in:
Alexey Kuznetsov 2006-09-19 12:52:50 -07:00 committed by David S. Miller
parent 4eb327b517
commit 1ef9696c90
3 changed files with 9 additions and 3 deletions
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3
include/net/inet_connection_sock.h
View File

@ -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,

7
net/ipv4/tcp.c
View File

@ -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;
}

2
net/ipv4/tcp_input.c
View File

@ -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;
}
}