Interesting iperf UDP behaviour with new kernel/Linux release

Discussion in 'Linux Networking' started by, Jul 8, 2014.

  1. Guest


    I'm trying to figure out what is causing iperf UDP test to some kind of 'flow controlled' with the new Fedora 18/Kernel 3.x.

    I tested with the same iperf v2.0.5, same command on the client side:

    iperf -c _server_ip_addr -u -b 4000m -i 1

    With Fedora 14, the client side shows 4Gbps of packets are pushed to the driver and the server side shows huge packet loss. With Fedora 18, the clientside seems automatically adjusts its TX rate to the capacity of the link and the server side shows almost 0 packet loss.

    I'm very curious what is changed between Fedora 14 and Fedora 18 to give UDP such a different behaviour, and is it the future of UDP implementation?

, Jul 8, 2014
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    Rick Jones Guest

    My experience with netperf and its UDP_STREAM test is that Linux has
    had "intra stack" flow control for a Very Long Time (tm). If the
    process tried to send outbound UDP traffic faster than the link could
    send it, it would get flow-controlled. From time to time there may
    have been bugs in that where it might get broken of course...

    rick jones
    Rick Jones, Jul 8, 2014
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