Questions about Infiniband on FreeBSD

[Mikhail T.]

Hello! After some wrangling, I got the direct (no switch) Infiniband 
connection working reliably between my two servers (a dual port mlx4 
card in each). I have the following questions:

 1. Why is running opensm mandatory even in a "point-to-point" setup
    like mine? I would've thought, whatever the two ends need to tell
    each other could be told /once/, after which the connection will
    continue to work even if the opensm-process goes away.
    Unfortunately, shutting down opensm freezes the connection... Is
    that a hardware/firmware requirement, or can this be improved?
 2. Although pings were working and NFS would mount, data-transfers
    weren't reliable until I /manually/ lowered the MTU -- on both ends
    -- to 2044 (from the 65520 used by the ib-interfaces by default).
    And it only occurred to me to do that, when I saw a kernel's message
    on one of the two consoles complaining about a packet length of 16k
    being greater than 2044... If that's a known limit, why is not the
    MTU set to it by default?
 3. Currently, I have only one cable connecting the ib1 on one machine
    to ib1 of another. Would I get double the throughput if I connect
    the two other ports together as well and bundle the connections? If
    yes, should I bundle them as network-interfaces -- using lagg(4) --
    or is there something Infiniband-specific?
 4. Mellanox recommends keeping the cards' firmware up-to-date. Does
    FreeBSD have a tool to do that?

Thank you very much. Yours,

    -mi