[TCP]: Send ACKs each 2nd received segment.
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>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 29e3d60..66e9a72 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -955,8 +955,11 @@
* 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;
}