net: add document for several snmp counters
add document for below counters: TcpEstabResets TcpAttemptFails TcpOutRsts TcpExtTCPSACKDiscard TcpExtTCPDSACKIgnoredOld TcpExtTCPDSACKIgnoredNoUndo TcpExtTCPSackShifted TcpExtTCPSackMerged TcpExtTCPSackShiftFallback TcpExtTCPWantZeroWindowAdv TcpExtTCPToZeroWindowAdv TcpExtTCPFromZeroWindowAdv TcpExtDelayedACKs TcpExtDelayedACKLocked TcpExtDelayedACKLost TcpExtTCPLossProbes TcpExtTCPLossProbeRecovery Signed-off-by: yupeng <yupeng0921@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>hifive-unleashed-5.1
yupeng
David S. Miller
parent
26fc181e6c
commit
a6c7c7aac2
|
|
@ -336,7 +336,26 @@ time client replies ACK, this socket will get another chance to move
|
|||
to the accept queue.
|
||||
|
||||
|
||||
TCP Fast Open
|
||||
* TcpEstabResets
|
||||
Defined in `RFC1213 tcpEstabResets`_.
|
||||
|
||||
.. _RFC1213 tcpEstabResets: https://tools.ietf.org/html/rfc1213#page-48
|
||||
|
||||
* TcpAttemptFails
|
||||
Defined in `RFC1213 tcpAttemptFails`_.
|
||||
|
||||
.. _RFC1213 tcpAttemptFails: https://tools.ietf.org/html/rfc1213#page-48
|
||||
|
||||
* TcpOutRsts
|
||||
Defined in `RFC1213 tcpOutRsts`_. The RFC says this counter indicates
|
||||
the 'segments sent containing the RST flag', but in linux kernel, this
|
||||
couner indicates the segments kerenl tried to send. The sending
|
||||
process might be failed due to some errors (e.g. memory alloc failed).
|
||||
|
||||
.. _RFC1213 tcpOutRsts: https://tools.ietf.org/html/rfc1213#page-52
|
||||
|
||||
|
||||
TCP Fast Path
|
||||
============
|
||||
When kernel receives a TCP packet, it has two paths to handler the
|
||||
packet, one is fast path, another is slow path. The comment in kernel
|
||||
|
|
@ -383,8 +402,6 @@ increase 1.
|
|||
|
||||
TCP abort
|
||||
========
|
||||
|
||||
|
||||
* TcpExtTCPAbortOnData
|
||||
It means TCP layer has data in flight, but need to close the
|
||||
connection. So TCP layer sends a RST to the other side, indicate the
|
||||
|
|
@ -545,7 +562,6 @@ packet yet, the sender would know packet 4 is out of order. The TCP
|
|||
stack of kernel will increase TcpExtTCPSACKReorder for both of the
|
||||
above scenarios.
|
||||
|
||||
|
||||
DSACK
|
||||
=====
|
||||
The DSACK is defined in `RFC2883`_. The receiver uses DSACK to report
|
||||
|
|
@ -566,13 +582,63 @@ The TCP stack receives an out of order duplicate packet, so it sends a
|
|||
DSACK to the sender.
|
||||
|
||||
* TcpExtTCPDSACKRecv
|
||||
The TCP stack receives a DSACK, which indicate an acknowledged
|
||||
The TCP stack receives a DSACK, which indicates an acknowledged
|
||||
duplicate packet is received.
|
||||
|
||||
* TcpExtTCPDSACKOfoRecv
|
||||
The TCP stack receives a DSACK, which indicate an out of order
|
||||
duplicate packet is received.
|
||||
|
||||
invalid SACK and DSACK
|
||||
====================
|
||||
When a SACK (or DSACK) block is invalid, a corresponding counter would
|
||||
be updated. The validation method is base on the start/end sequence
|
||||
number of the SACK block. For more details, please refer the comment
|
||||
of the function tcp_is_sackblock_valid in the kernel source code. A
|
||||
SACK option could have up to 4 blocks, they are checked
|
||||
individually. E.g., if 3 blocks of a SACk is invalid, the
|
||||
corresponding counter would be updated 3 times. The comment of the
|
||||
`Add counters for discarded SACK blocks`_ patch has additional
|
||||
explaination:
|
||||
|
||||
.. _Add counters for discarded SACK blocks: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=18f02545a9a16c9a89778b91a162ad16d510bb32
|
||||
|
||||
* TcpExtTCPSACKDiscard
|
||||
This counter indicates how many SACK blocks are invalid. If the invalid
|
||||
SACK block is caused by ACK recording, the TCP stack will only ignore
|
||||
it and won't update this counter.
|
||||
|
||||
* TcpExtTCPDSACKIgnoredOld and TcpExtTCPDSACKIgnoredNoUndo
|
||||
When a DSACK block is invalid, one of these two counters would be
|
||||
updated. Which counter will be updated depends on the undo_marker flag
|
||||
of the TCP socket. If the undo_marker is not set, the TCP stack isn't
|
||||
likely to re-transmit any packets, and we still receive an invalid
|
||||
DSACK block, the reason might be that the packet is duplicated in the
|
||||
middle of the network. In such scenario, TcpExtTCPDSACKIgnoredNoUndo
|
||||
will be updated. If the undo_marker is set, TcpExtTCPDSACKIgnoredOld
|
||||
will be updated. As implied in its name, it might be an old packet.
|
||||
|
||||
SACK shift
|
||||
=========
|
||||
The linux networking stack stores data in sk_buff struct (skb for
|
||||
short). If a SACK block acrosses multiple skb, the TCP stack will try
|
||||
to re-arrange data in these skb. E.g. if a SACK block acknowledges seq
|
||||
10 to 15, skb1 has seq 10 to 13, skb2 has seq 14 to 20. The seq 14 and
|
||||
15 in skb2 would be moved to skb1. This operation is 'shift'. If a
|
||||
SACK block acknowledges seq 10 to 20, skb1 has seq 10 to 13, skb2 has
|
||||
seq 14 to 20. All data in skb2 will be moved to skb1, and skb2 will be
|
||||
discard, this operation is 'merge'.
|
||||
|
||||
* TcpExtTCPSackShifted
|
||||
A skb is shifted
|
||||
|
||||
* TcpExtTCPSackMerged
|
||||
A skb is merged
|
||||
|
||||
* TcpExtTCPSackShiftFallback
|
||||
A skb should be shifted or merged, but the TCP stack doesn't do it for
|
||||
some reasons.
|
||||
|
||||
TCP out of order
|
||||
===============
|
||||
* TcpExtTCPOFOQueue
|
||||
|
|
@ -662,6 +728,60 @@ unacknowledged number (more strict than `RFC 5961 section 5.2`_).
|
|||
.. _RFC 5961 section 4.2: https://tools.ietf.org/html/rfc5961#page-9
|
||||
.. _RFC 5961 section 5.2: https://tools.ietf.org/html/rfc5961#page-11
|
||||
|
||||
TCP receive window
|
||||
=================
|
||||
* TcpExtTCPWantZeroWindowAdv
|
||||
Depending on current memory usage, the TCP stack tries to set receive
|
||||
window to zero. But the receive window might still be a no-zero
|
||||
value. For example, if the previous window size is 10, and the TCP
|
||||
stack receives 3 bytes, the current window size would be 7 even if the
|
||||
window size calculated by the memory usage is zero.
|
||||
|
||||
* TcpExtTCPToZeroWindowAdv
|
||||
The TCP receive window is set to zero from a no-zero value.
|
||||
|
||||
* TcpExtTCPFromZeroWindowAdv
|
||||
The TCP receive window is set to no-zero value from zero.
|
||||
|
||||
|
||||
Delayed ACK
|
||||
==========
|
||||
The TCP Delayed ACK is a technique which is used for reducing the
|
||||
packet count in the network. For more details, please refer the
|
||||
`Delayed ACK wiki`_
|
||||
|
||||
.. _Delayed ACK wiki: https://en.wikipedia.org/wiki/TCP_delayed_acknowledgment
|
||||
|
||||
* TcpExtDelayedACKs
|
||||
A delayed ACK timer expires. The TCP stack will send a pure ACK packet
|
||||
and exit the delayed ACK mode.
|
||||
|
||||
* TcpExtDelayedACKLocked
|
||||
A delayed ACK timer expires, but the TCP stack can't send an ACK
|
||||
immediately due to the socket is locked by a userspace program. The
|
||||
TCP stack will send a pure ACK later (after the userspace program
|
||||
unlock the socket). When the TCP stack sends the pure ACK later, the
|
||||
TCP stack will also update TcpExtDelayedACKs and exit the delayed ACK
|
||||
mode.
|
||||
|
||||
* TcpExtDelayedACKLost
|
||||
It will be updated when the TCP stack receives a packet which has been
|
||||
ACKed. A Delayed ACK loss might cause this issue, but it would also be
|
||||
triggered by other reasons, such as a packet is duplicated in the
|
||||
network.
|
||||
|
||||
Tail Loss Probe (TLP)
|
||||
===================
|
||||
TLP is an algorithm which is used to detect TCP packet loss. For more
|
||||
details, please refer the `TLP paper`_.
|
||||
|
||||
.. _TLP paper: https://tools.ietf.org/html/draft-dukkipati-tcpm-tcp-loss-probe-01
|
||||
|
||||
* TcpExtTCPLossProbes
|
||||
A TLP probe packet is sent.
|
||||
|
||||
* TcpExtTCPLossProbeRecovery
|
||||
A packet loss is detected and recovered by TLP.
|
||||
|
||||
examples
|
||||
=======
|
||||
|
|
|
|||
Loading…
Reference in New Issue