tcp_slow_start_* tunables should allow increasing the initial congestion window
The current implementation of initial congestion window calculation uses RFC 3390 correctly, but in the event the operator wants to violate the RFC for a fast TCP start (initial congestion window of 10) re: http://research.google.com/pubs/pub36640.html it cannot be done except for programmatically via setsockopt.
Setting the two tunables should allow the operator to increase the initial congestion window up within reason. The implementation of TCP_INIT_CWND via setsockopt has a "sane" maximum of 16, that should be adopted.
The tunables: tcp_slow_start_initial and tcp_slow_start_after_idle should change in behaviour. They should default to 0, which takes on the new meaning of strict adherence to RFC 3390 and if there are set to a number larger than 0, then the initial congestion window (or restart after idle) is set directly to that specified value. The allowable ranges of the two tunables should remain unchanged (sans allowing 0 for "default" behavior).