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Subject[PATCH] docs: net: Remove TCP congestion document
Document is stale, let's remove it.

Remove TCP congestion document.

Signed-off-by: Tobin C. Harding <>

Previous patch converted this file to rst.

[PATCH RESEND net-next] docs: net: Convert tcp.txt to RST format

Response to that patch on LKML by Eric:

I dunno, this 'doc' is probably useless and should be deleted.

Removing as suggested.


Documentation/networking/00-INDEX | 2 -
Documentation/networking/tcp.txt | 101 ------------------------------
2 files changed, 103 deletions(-)
delete mode 100644 Documentation/networking/tcp.txt

diff --git a/Documentation/networking/00-INDEX b/Documentation/networking/00-INDEX
index 02a323c43261..dcbccae4043e 100644
--- a/Documentation/networking/00-INDEX
+++ b/Documentation/networking/00-INDEX
@@ -198,8 +198,6 @@ tc-actions-env-rules.txt
- rules for traffic control (tc) actions.
- overview of network packet timestamping variants.
- - short blurb on how TCP output takes place.
- kernel tuning options for low rate 'thin' TCP streams.
diff --git a/Documentation/networking/tcp.txt b/Documentation/networking/tcp.txt
deleted file mode 100644
index 9c7139d57e57..000000000000
--- a/Documentation/networking/tcp.txt
+++ /dev/null
@@ -1,101 +0,0 @@
-TCP protocol
-Last updated: 3 June 2017
-- Congestion control
-- How the new TCP output machine [nyi] works
-Congestion control
-The following variables are used in the tcp_sock for congestion control:
-snd_cwnd The size of the congestion window
-snd_ssthresh Slow start threshold. We are in slow start if
- snd_cwnd is less than this.
-snd_cwnd_cnt A counter used to slow down the rate of increase
- once we exceed slow start threshold.
-snd_cwnd_clamp This is the maximum size that snd_cwnd can grow to.
-snd_cwnd_stamp Timestamp for when congestion window last validated.
-snd_cwnd_used Used as a highwater mark for how much of the
- congestion window is in use. It is used to adjust
- snd_cwnd down when the link is limited by the
- application rather than the network.
-As of 2.6.13, Linux supports pluggable congestion control algorithms.
-A congestion control mechanism can be registered through functions in
-tcp_cong.c. The functions used by the congestion control mechanism are
-registered via passing a tcp_congestion_ops struct to
-tcp_register_congestion_control. As a minimum, the congestion control
-mechanism must provide a valid name and must implement either ssthresh,
-cong_avoid and undo_cwnd hooks or the "omnipotent" cong_control hook.
-Private data for a congestion control mechanism is stored in tp->ca_priv.
-tcp_ca(tp) returns a pointer to this space. This is preallocated space - it
-is important to check the size of your private data will fit this space, or
-alternatively, space could be allocated elsewhere and a pointer to it could
-be stored here.
-There are three kinds of congestion control algorithms currently: The
-simplest ones are derived from TCP reno (highspeed, scalable) and just
-provide an alternative congestion window calculation. More complex
-ones like BIC try to look at other events to provide better
-heuristics. There are also round trip time based algorithms like
-Vegas and Westwood+.
-Good TCP congestion control is a complex problem because the algorithm
-needs to maintain fairness and performance. Please review current
-research and RFC's before developing new modules.
-The default congestion control mechanism is chosen based on the
-DEFAULT_TCP_CONG Kconfig parameter. If you really want a particular default
-value then you can set it using sysctl net.ipv4.tcp_congestion_control. The
-module will be autoloaded if needed and you will get the expected protocol. If
-you ask for an unknown congestion method, then the sysctl attempt will fail.
-If you remove a TCP congestion control module, then you will get the next
-available one. Since reno cannot be built as a module, and cannot be
-removed, it will always be available.
-How the new TCP output machine [nyi] works.
-Data is kept on a single queue. The skb->users flag tells us if the frame is
-one that has been queued already. To add a frame we throw it on the end. Ack
-walks down the list from the start.
-We keep a set of control flags
- sk->tcp_pend_event
- TCP_PEND_ACK Ack needed
- TCP_ACK_NOW Needed now
- TCP_WINDOW Window update check
- TCP_WINZERO Zero probing
- sk->transmit_queue The transmission frame begin
- sk->transmit_new First new frame pointer
- sk->transmit_end Where to add frames
- sk->tcp_last_tx_ack Last ack seen
- sk->tcp_dup_ack Dup ack count for fast retransmit
-Frames are queued for output by tcp_write. We do our best to send the frames
-off immediately if possible, but otherwise queue and compute the body
-checksum in the copy.
-When a write is done we try to clear any pending events and piggy back them.
-If the window is full we queue full sized frames. On the first timeout in
-zero window we split this.
-On a timer we walk the retransmit list to send any retransmits, update the
-backoff timers etc. A change of route table stamp causes a change of header
-and recompute. We add any new tcp level headers and refinish the checksum
-before sending.
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