In some cases rack end up with an incorrect RTT set initially. In particular
the test case is where we have a long RTT, the server sends the
initial message after the 3-way handshake. Srtt and rttvar
end up the correct values, but tp->t_rtxcur does not. Usually
quite a smaller value. This causes all kinds of trouble in 2 TLP's and
finally a RXT that knock the cwnd to 1 MSS. The consequences
of this are the connection crawls.
What should be happening is we call the proper t_rxtcur set macro
after setting up properly the srtt and rttvar.