Set the default send and receive socket buffer size to 0,
which means Open MPI will not try to set a buffer size during
startup.
The default behavior since near day one of the TCP BTL has been
to set the send and receive socket buffer sizes to 128 KiB. A
number that works great on 1 GbE, but not so great on 10 GbE
fabrics of any real size. Modern TCP stacks, particularly on
Linux, have gotten much smarter about buffer sizes and are much
less efficient if a buffer size is set (even if set to something
large).
Signed-off-by: Brian Barrett <bbarrett@amazon.com>
3b991498be