Document is stale, let's remove it. Remove TCP congestion document. Signed-off-by: Tobin C. Harding <me@xxxxxxxx> --- 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. thanks, Tobin. 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. timestamping.txt - overview of network packet timestamping variants. -tcp.txt - - short blurb on how TCP output takes place. tcp-thin.txt - kernel tuning options for low rate 'thin' TCP streams. team.txt 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 - -Contents -======== - -- 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. - -- 2.17.1
