Include scripts to help determine correct value for TCP receive buffers

[eflumerf]

This issue has been migrated from https://cdcvs.fnal.gov/redmine/issues/15619 (FNAL account required)
Originally created by @eflumerf on 2017-02-21 20:27:47

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The TCPSocket_transfer class uses either a manually-set receive buffer or the kernel autotuning. We should provide scripts/tools to help determine the correct manual setting for a given DAQ envrionment.

[ron003]

Just some comments on this...
we could try to run a series of artdaq-demos in a wrapper script that uses rgang to get the initial and ending retransmission counts for the boardreader nodes. Also, on the event builder nodes, different values for RCVBUF would be tried. NOTE: a RCVBUF size that allows for at least 10 MTU-sized packets should be used to avoid the rare case where all packets associated with a window are dropped.
Large (9K) MTUs (jumbo packets) can hinder this area. Another factor that comes into play is the number of event builder processes running on each event builder. They multiply the amount of potential data in flight and therefore would necessitate decreasing the RCVBUF size.