Documentation/networking/snmp_counter.rst

330   retransmissions into SYN, fast-retransmits, timeout retransmits, etc.
337   TCPFastOpenActiveFail: Fast Open attempts (SYN/data) failed because
365 TCP Fast Open
413 TCP Fast Path
416 packet, one is fast path, another is slow path. The comment in kernel
419   It is split into a fast path and a slow path. The fast path is
430   - Data is sent in both directions. The fast path only supports pure senders
435 Kernel will try to use fast path unless any of the above conditions
441 try to enable fast path immediately when the connection comes into the
443 will disable the fast path at first, and try to enable it after kernel
449 kernel handles it in the fast path, TcpExtTCPHPAcks will increase 1,
456 and this packet is handled in the fast path, TcpExtTCPHPHits will
568 The TCP protocol has two retransmission mechanisms: SACK and fast
570 the kernel TCP stack would use SACK, or kernel would use fast
572 the fast recovery is defined in `RFC6582`_, which is also called
605 The reorder packet is detected by fast recovery. It would only be used
606 if SACK is disabled. The fast recovery algorithm detects recorder by
907 TCP Fast Open description
909 TCP Fast Open is a technology which allows data transfer before the
910 3-way handshake complete. Please refer the `TCP Fast Open wiki`_ for a
913 .. _TCP Fast Open wiki: https://en.wikipedia.org/wiki/TCP_Fast_Open
924 This counter indicates that the TCP stack initiated a TCP Fast Open,
930 fast open after the handshake.
934 This counter indicates how many times the TCP stack accepts the fast
939 This counter indicates how many times the TCP stack rejects the fast
945 When the pending fast open request number is larger than
946 fastopenq->max_qlen, the TCP stack will reject the fast open request
1207 TCP window scale option is not used, kernel will try to enable fast
1210 fast path at first, and try to enable it after kernel receives
1224 reply an ACK, when kernel handled this ACK, the fast path was not
1228 and received another ACK from the server, in this time, the fast path is
1229 enabled, and the ACK was qualified for fast path, so it was handled by
1230 the fast path, so this ACK was counted into TcpExtTCPHPAcks.
1232 In the first nstat output of server side, fast path was not enabled,
1235 In the second nstat output of server side, the fast path was enabled,
1236 and the packet received from client qualified for fast path, so it