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Thread: Poor bidirectional iperf speed in Windows

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    Senior Member watercooled's Avatar
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    Poor bidirectional iperf speed in Windows

    This seems to be a common problem with Windows but I can't seem to find out much about it online.

    When I run the following command on Windows,
    iperf -c iphere -w 256k -d
    the combined bidirectional speed is fairly poor, often under 1000Mb/s total but if I boot the same system into Linux it's closer to 2000Mb/s like you'd expect. Unidirectional speed seems fine.

    According to Resource Monitor, System Interrupts is maxing a CPU core which is likely the cause of the bottleneck, but it doesn't explain why it's fine under Linux, or why my Microserver (also running Linux) is also fine despite using a much slower CPU.

    I've checked, and checksum offload, interrupt moderation etc are all enabled. Same happens with both Intel NIC and onboard Realtek.

    Same problem happens on my Thuban system; performance is closer to what you'd expect but still not as fast as Linux on my Microserver...

    Update: Considering the Windows version of iperf is fairly outdated, I tried the Linux version in cygwin which did improve performance somewhat. Still not up there with Linux performance, but it is improved + repeatable.
    Last edited by watercooled; 13-09-2012 at 09:09 PM.

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