For the "everything old is new again" files, back in the 1990s, it was
noticed that on the likes of a netperf UDP_STREAM test on HP-UX, with
fragmentation taking place, it was possible to consume 100% of the link
bandwidth and have 0% effective throughput because the transmit queue
was kept full with IP datagram fragments which could not possibly be
reassembled (*) because one or more of the fragments of a datagram were
dropped because the transmit queue was full.
HP-UX implemented "packet trains" where all the fragments of a
fragmented datagram were presented to the driver, which then either
queued them all, or none of them.
I don't recall seeing similar poor behaviour in Linux; I would have
assumed that the intra-stack flow-control "took care" of it. Perhaps
there is something specific to wpan which precludes that?
happy benchmarking,
rick jones
