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| author | Christoph Paasch <cpaasch@apple.com> | 2020-05-14 08:53:03 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2020-05-16 13:51:10 -0700 |
| commit | a0c1d0eafd1ef1ada3b588ea205e5bc37ae0d8d9 (patch) | |
| tree | 9e6c4e1406a00559b1dd4ef04cf502d65e5cb3e7 /net/mptcp/options.c | |
| parent | 9efd6a3cecdde984d67e63d17fe6af53c7c50968 (diff) | |
| download | lwn-a0c1d0eafd1ef1ada3b588ea205e5bc37ae0d8d9.tar.gz lwn-a0c1d0eafd1ef1ada3b588ea205e5bc37ae0d8d9.zip | |
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 <cpaasch@apple.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/mptcp/options.c')
| -rw-r--r-- | net/mptcp/options.c | 33 |
1 files changed, 24 insertions, 9 deletions
diff --git a/net/mptcp/options.c b/net/mptcp/options.c index 45497af23906..ece6f92cf7d1 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -516,7 +516,16 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb, return ret; } - ack_size = TCPOLEN_MPTCP_DSS_ACK64; + if (subflow->use_64bit_ack) { + ack_size = TCPOLEN_MPTCP_DSS_ACK64; + opts->ext_copy.data_ack = msk->ack_seq; + opts->ext_copy.ack64 = 1; + } else { + ack_size = TCPOLEN_MPTCP_DSS_ACK32; + opts->ext_copy.data_ack32 = (uint32_t)(msk->ack_seq); + opts->ext_copy.ack64 = 0; + } + opts->ext_copy.use_ack = 1; /* Add kind/length/subtype/flag overhead if mapping is not populated */ if (dss_size == 0) @@ -524,10 +533,6 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb, dss_size += ack_size; - opts->ext_copy.data_ack = msk->ack_seq; - opts->ext_copy.ack64 = 1; - opts->ext_copy.use_ack = 1; - *size = ALIGN(dss_size, 4); return true; } @@ -986,8 +991,13 @@ mp_capable_done: u8 flags = 0; if (mpext->use_ack) { - len += TCPOLEN_MPTCP_DSS_ACK64; - flags = MPTCP_DSS_HAS_ACK | MPTCP_DSS_ACK64; + flags = MPTCP_DSS_HAS_ACK; + if (mpext->ack64) { + len += TCPOLEN_MPTCP_DSS_ACK64; + flags |= MPTCP_DSS_ACK64; + } else { + len += TCPOLEN_MPTCP_DSS_ACK32; + } } if (mpext->use_map) { @@ -1004,8 +1014,13 @@ mp_capable_done: *ptr++ = mptcp_option(MPTCPOPT_DSS, len, 0, flags); if (mpext->use_ack) { - put_unaligned_be64(mpext->data_ack, ptr); - ptr += 2; + if (mpext->ack64) { + put_unaligned_be64(mpext->data_ack, ptr); + ptr += 2; + } else { + put_unaligned_be32(mpext->data_ack32, ptr); + ptr += 1; + } } if (mpext->use_map) { |