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Date: Wed, 4 May 2022 14:54:03 -0700 From: Mat Martineau <mathew.j.martineau@...ux.intel.com> To: netdev@...r.kernel.org Cc: Mat Martineau <mathew.j.martineau@...ux.intel.com>, davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com, matthieu.baerts@...sares.net, mptcp@...ts.linux.dev Subject: [PATCH net-next 0/5] mptcp: Improve MPTCP-level window tracking This series improves MPTCP receive window compliance with RFC 8684 and helps increase throughput on high-speed links. Note that patch 3 makes a change in tcp_output.c For the details, Paolo says: I've been chasing bad/unstable performance with multiple subflows on very high speed links. It looks like the root cause is due to the current mptcp-level congestion window handling. There are apparently a few different sub-issues: - the rcv_wnd is not effectively shared on the tx side, as each subflow takes in account only the value received by the underlaying TCP connection. This is addressed in patch 1/4 - The mptcp-level offered wnd right edge is currently allowed to shrink. Reading section 3.3.4.: """ The receive window is relative to the DATA_ACK. As in TCP, a receiver MUST NOT shrink the right edge of the receive window (i.e., DATA_ACK + receive window). The receiver will use the data sequence number to tell if a packet should be accepted at the connection level. """ I read the above as we need to reflect window right-edge tracking on the wire, see patch 4/5. - The offered window right edge tracking can happen concurrently on multiple subflows, but there is no mutex protection. We need an additional atomic operation - still patch 3/4 This series additionally bumps a few new MIBs to track all the above (ensure/observe that the suspected races actually take place). I could not access again the host where the issue was so noticeable, still in the current setup the tput changes from [6-18] Gbps to 19Gbps very stable. Paolo Abeni (5): mptcp: really share subflow snd_wnd mptcp: add mib for xmit window sharing tcp: allow MPTCP to update the announced window mptcp: never shrink offered window mptcp: add more offered MIBs counter include/net/mptcp.h | 2 +- net/ipv4/tcp_output.c | 14 ++++++----- net/mptcp/mib.c | 4 +++ net/mptcp/mib.h | 6 +++++ net/mptcp/options.c | 58 +++++++++++++++++++++++++++++++++++++------ net/mptcp/protocol.c | 32 +++++++++++++++--------- net/mptcp/protocol.h | 2 +- 7 files changed, 90 insertions(+), 28 deletions(-) base-commit: a37f37a2e7f5ea3ae2a1278f552aa21a8e32c221 -- 2.36.0
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