[ replying here because gmail is broken ] > > How high is too high? I have a utility that sets recv buf size > > to 100,000,000 and it works fine on FreeBSD and NetBSD. (Not > > tested yet on OpenBSD.) Necessary when the other end has buggy > > network code and insufficient send buf. > > Could you clarify what you mean by that?
Black box sends data to BSD box using TCP. Data is generated in real time, the rate cannot be changed. Black box has a very small (way too small) send buffer. If the BSD box takes too long to ack, the black box's send buffer fills up and data is lost, and/or black box's buggy firmware screws up and data is lost. So I have to do everything I can to ensure that incoming packets do not get dropped, and that the acks get sent out as fast as possible. Making the TCP recv buffer very large allows the incoming packets to get stored and acked, even if the userland process reading the data doesn't get to run often enough. Even so, there is still the problem that other device drivers can and do lock out the Ethernet driver for too long. Still working on that problem. What we really need is true real time facilities. It is a latency problem, not a throughput problem. If the black box were FLOSS instead of evil closed source it should be possible to fix the buggy network code.
