+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 the 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 method that is used to determine which congestion control mechanism is
+determined by the setting of the sysctl net.ipv4.tcp_congestion_control.
+The default congestion control will be the last one registered (LIFO);
+so if you built everything as modules, the default will be reno. If you
+build with the defaults from Kconfig, then CUBIC will be builtin (not a
+module) and it will end up the default.
+
+If you really want a particular default value then you will need
+to set it with the sysctl. If you use a sysctl, 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
+deleted, it will always be available.
+
+How the new TCP output machine [nyi] works.
+===========================================