Are you talking about TCP_RTO_MIN? I seem to believe this is hard coded in the kernel to 200 Milliseconds. Under the workload I have tested, huge gains were had by just changing this value to 10 miliseconds.
It would be great if this was configurable or lowered ... as the 200 miliseconds seems to cause a real bottleneck in some cases.
Does anyone know if this has been proposed or is being made configurable?