Subject: Re: [patch] add tcp congestion control relevant parts

From: Michael Kerrisk <[email-masked]>
Date: Fri, 14 Dec 2007 09:48:32 +0100

Hello Linux networking folk,

I received the patch below for the tcp.7 man page.  Would anybody here be
prepared to review the new material / double check the details?

Cheers,

Michael

-------- Original Message --------
Subject: [patch] add tcp congestion control relevant parts
Date: Wed, 12 Dec 2007 16:40:23 +0100
From: Thomas Egerer <[email-masked]>
To: [email-masked]
CC: [email-masked]

Hello *,

man-pages version : 2.70 from http://www.kernel.org/pub/linux/docs/man-pages/
All required information were obtained by reading the kernel
code/documentation.
I'm not sure, whether it is completely bullet proof on when the sysctl
variables/socket option first appeared in the kernel, so you might as well
drop this information, but I'm pretty sure about how it works.
Here we go with my patch:

diff -ru man-pages-2.70/man7/tcp.7 man-pages-2.70.new/man7/tcp.7
--- man-pages-2.70/man7/tcp.7   2007-11-24 14:33:34.000000000 +0100
+++ man-pages-2.70.new/man7/tcp.7       2007-12-12 16:34:52.000000000 +0100
@@ -177,8 +177,6 @@
 .\" FIXME As at Sept 2006, kernel 2.6.18-rc5, the following are
 .\"    not yet documented (shown with default values):
 .\"
-.\"     /proc/sys/net/ipv4/tcp_congestion_control (since 2.6.13)
-.\"     bic
 .\"     /proc/sys/net/ipv4/tcp_moderate_rcvbuf
 .\"     1
 .\"     /proc/sys/net/ipv4/tcp_no_metrics_save
@@ -224,6 +222,20 @@
 are reserved for the application buffer.
 A value of 0
 implies that no amount is reserved.
+.TP
+.BR tcp_allowed_congestion_control \
+" (String; default: cubic reno) (since 2.6.13) "
+Show/set the congestion control choices available to non-privileged
+processes. The list is a subset of those listed in
+.IR tcp_available_congestion_control "."
+Default is "cubic reno" and the default setting
+.RI ( tcp_congestion_control ).
+.TP
+.BR tcp_available_congestion_control \
+" (String; default: cubic reno) (since 2.6.13) "
+Lists the TCP congestion control algorithms available on the system. This
value
+can only be changed by loading/unloading modules responsible for congestion
+control.
 .\"
 .\" The following is from 2.6.12: Documentation/networking/ip-sysctl.txt
 .TP
@@ -257,6 +269,17 @@
 Allows two flows sharing the same connection to converge
 more rapidly.
 .TP
+.BR tcp_congestion_control " (String; default: cubic reno) (since 2.6.13) "
+Determines the congestion control algorithm used for newly created TCP
+sockets. By default Linux uses cubic with reno as fallback. If you want
+to have more control over the algorithm used, you must enable the symbol
+CONFIG_TCP_CONG_ADVANCED in your kernel config.
+You can use
+.BR setsockopt (2)
+to individually change the algorithm on a single socket.
+Requires CAP_NET_ADMIN or congestion algorithm to be listed in
+.IR tcp_allowed_congestion_control "."
+.TP
 .BR tcp_dsack " (Boolean; default: enabled)"
 Enable RFC\ 2883 TCP Duplicate SACK support.
 .TP
@@ -649,7 +672,21 @@
 socket options are valid on TCP sockets.
 For more information see
 .BR ip (7).
-.\" FIXME Document TCP_CONGESTION (new in 2.6.13)
+.TP
+.BR TCP_CONGESTION " (new since kernel version 2.6.13)"
+If set to the name of an available congestion control algorithm,
+it will henceforth be used for the socket. To get a list of
+available congestion control algorithms, consult the sysctl variable
+.IR net.ipv4.tcp_available_congestion_control "."
+The algorithm that is used by default for all newly created
+TCP sockets can be viewed/changed via the sysctl variable
+.IR net.ipv4.tcp_congestion_control "."
+If you feel, you are missing an algorithm in the list,
+you may try to load the corresponding module using
+.BR modprobe (8),
+or if your kernel is built with module autoloading support
+.RI ( CONFIG_KMOD )
+and the algorithm has been compiled as a module, it will be autoloaded.
 .TP
 .B TCP_CORK
 If set, don't send out partial frames.

-- 
Michael Kerrisk
Maintainer of the Linux man-pages project
http://www.kernel.org/doc/man-pages/
Want to report a man-pages bug?  Look here:
http://www.kernel.org/doc/man-pages/reporting_bugs.html