diff options
| author | Yuchung Cheng <ycheng@google.com> | 2018-08-09 09:38:12 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2018-08-11 11:31:35 -0700 |
| commit | fd2123a3d7527d4c7092633d55e877c0cc1d84a3 (patch) | |
| tree | 409e7e277b55816d4afd45263fb45146c07e02bb /net/ipv4 | |
| parent | 15bdd5686c2c61373680b9015e95abf31778e4fd (diff) | |
| download | linux-fd2123a3d7527d4c7092633d55e877c0cc1d84a3.tar.bz2 | |
tcp: avoid resetting ACK timer upon receiving packet with ECN CWR flag
Previously commit 9aee40006190 ("tcp: ack immediately when a cwr
packet arrives") calls tcp_enter_quickack_mode to force sending
two immediate ACKs upon receiving a packet w/ CWR flag. The side
effect is it'll also reset the delayed ACK timer and interactive
session tracking. This patch removes that side effect by using the
new ACK_NOW flag to force an immmediate ACK.
Packetdrill to demonstrate:
0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+0 setsockopt(3, SOL_TCP, TCP_CONGESTION, "dctcp", 5) = 0
+0 bind(3, ..., ...) = 0
+0 listen(3, 1) = 0
+0 < [ect0] SEW 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
+0 > SE. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
+.1 < [ect0] . 1:1(0) ack 1 win 257
+0 accept(3, ..., ...) = 4
+0 < [ect0] . 1:1001(1000) ack 1 win 257
+0 > [ect01] . 1:1(0) ack 1001
+0 write(4, ..., 1) = 1
+0 > [ect01] P. 1:2(1) ack 1001
+0 < [ect0] . 1001:2001(1000) ack 2 win 257
+0 write(4, ..., 1) = 1
+0 > [ect01] P. 2:3(1) ack 2001
+0 < [ect0] . 2001:3001(1000) ack 3 win 257
+0 < [ect0] . 3001:4001(1000) ack 3 win 257
// Ack delayed ...
+.01 < [ce] P. 4001:4501(500) ack 3 win 257
+0 > [ect01] . 3:3(0) ack 4001
+0 > [ect01] E. 3:3(0) ack 4501
+.001 read(4, ..., 4500) = 4500
+0 write(4, ..., 1) = 1
+0 > [ect01] PE. 3:4(1) ack 4501 win 100
+.01 < [ect0] W. 4501:5501(1000) ack 4 win 257
// No delayed ACK on CWR flag
+0 > [ect01] . 4:4(0) ack 5501
+.31 < [ect0] . 5501:6501(1000) ack 4 win 257
+0 > [ect01] . 4:4(0) ack 6501
Fixes: 9aee40006190 ("tcp: ack immediately when a cwr packet arrives")
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/tcp_input.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 9a09ff3afef2..4c2dd9f863f7 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -245,16 +245,16 @@ static void tcp_ecn_queue_cwr(struct tcp_sock *tp) tp->ecn_flags |= TCP_ECN_QUEUE_CWR; } -static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb) +static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb) { if (tcp_hdr(skb)->cwr) { - tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; + tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR; /* If the sender is telling us it has entered CWR, then its * cwnd may be very low (even just 1 packet), so we should ACK * immediately. */ - tcp_enter_quickack_mode((struct sock *)tp, 2); + inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; } } @@ -4703,7 +4703,7 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) skb_dst_drop(skb); __skb_pull(skb, tcp_hdr(skb)->doff * 4); - tcp_ecn_accept_cwr(tp, skb); + tcp_ecn_accept_cwr(sk, skb); tp->rx_opt.dsack = 0; |