By the way, this isn't just theoretical -- I'm not smart enough to realize this except that I just saw: ib1: TX ring full, stopping kernel net queue NETDEV WATCHDOG: ib1: transmit timed out ib1: transmit timeout: latency 1240 msecs ib1: queue stopped 1, tx_head 5291313, tx_tail 5291255 and of course it never recovers.