From a0c1d0eafd1ef1ada3b588ea205e5bc37ae0d8d9 Mon Sep 17 00:00:00 2001 From: Christoph Paasch Date: Thu, 14 May 2020 08:53:03 -0700 Subject: mptcp: Use 32-bit DATA_ACK when possible RFC8684 allows to send 32-bit DATA_ACKs as long as the peer is not sending 64-bit data-sequence numbers. The 64-bit DSN is only there for extreme scenarios when a very high throughput subflow is combined with a long-RTT subflow such that the high-throughput subflow wraps around the 32-bit sequence number space within an RTT of the high-RTT subflow. It is thus a rare scenario and we should try to use the 32-bit DATA_ACK instead as long as possible. It allows to reduce the TCP-option overhead by 4 bytes, thus makes space for an additional SACK-block. It also makes tcpdumps much easier to read when the DSN and DATA_ACK are both either 32 or 64-bit. Signed-off-by: Christoph Paasch Reviewed-by: Matthieu Baerts Signed-off-by: David S. Miller --- net/mptcp/subflow.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'net/mptcp/subflow.c') diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 53c75b0e5dce..0020d356233d 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -667,9 +667,11 @@ static enum mapping_status get_mapping_status(struct sock *ssk) if (!mpext->dsn64) { map_seq = expand_seq(subflow->map_seq, subflow->map_data_len, mpext->data_seq); + subflow->use_64bit_ack = 0; pr_debug("expanded seq=%llu", subflow->map_seq); } else { map_seq = mpext->data_seq; + subflow->use_64bit_ack = 1; } if (subflow->map_valid) { -- cgit v1.2.3