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authorRandy Dunlap <rdunlap@infradead.org>2019-03-17 17:17:45 -0700
committerDavid S. Miller <davem@davemloft.net>2019-03-17 19:37:08 -0700
commit65e9a6d25deb752d97b88335068dc0e7accbc9c3 (patch)
treee7e44801df32ae5edca51a9ee65cc26fe00ae66f /Documentation
parent517ccc2aa50dbd7767a9eb8e1d9987a3ed7ced3e (diff)
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networking: fix snmp_counter.rst Doc. Warnings
Fix documentation markup warnings in snmp_counter.rst: Documentation/networking/snmp_counter.rst:416: WARNING: Title underline too short. Documentation/networking/snmp_counter.rst:684: WARNING: Bullet list ends without a blank line; unexpected unindent. Documentation/networking/snmp_counter.rst:693: WARNING: Title underline too short. Documentation/networking/snmp_counter.rst:707: WARNING: Bullet list ends without a blank line; unexpected unindent. Documentation/networking/snmp_counter.rst:712: WARNING: Bullet list ends without a blank line; unexpected unindent. Documentation/networking/snmp_counter.rst:722: WARNING: Title underline too short. Documentation/networking/snmp_counter.rst:733: WARNING: Bullet list ends without a blank line; unexpected unindent. Documentation/networking/snmp_counter.rst:736: WARNING: Bullet list ends without a blank line; unexpected unindent. Documentation/networking/snmp_counter.rst:739: WARNING: Bullet list ends without a blank line; unexpected unindent. Fixes: 80cc49507ba48 ("net: Add part of TCP counts explanations in snmp_counters.rst") Fixes: 8e2ea53a83dfb ("add snmp counters document") Fixes: a6c7c7aac2de6 ("net: add document for several snmp counters") Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Cc: yupeng <yupeng0921@gmail.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/networking/snmp_counter.rst12
1 files changed, 9 insertions, 3 deletions
diff --git a/Documentation/networking/snmp_counter.rst b/Documentation/networking/snmp_counter.rst
index 52b026be028f..38a4edc4522b 100644
--- a/Documentation/networking/snmp_counter.rst
+++ b/Documentation/networking/snmp_counter.rst
@@ -413,7 +413,7 @@ algorithm.
.. _F-RTO: https://tools.ietf.org/html/rfc5682
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
code provides a good explanation of them, I pasted them below::
@@ -681,6 +681,7 @@ 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 indicates an acknowledged
duplicate packet is received.
@@ -690,7 +691,7 @@ 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
@@ -704,11 +705,13 @@ 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
@@ -719,7 +722,7 @@ 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
@@ -730,12 +733,15 @@ 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.