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    SubjectRe: Brust data send problem on gigabit NIC on Linux
    Lk Overrun wrote:
    > Hi, I am seeking advice on how to best send out huge
    > number of packets on a gigabit ethernet interface. I
    > am using kernel 2.4.19. I try to send out as many as
    > possible 15Kbyte-long ethernet packets to try to
    > utilize the giga-bit/sec bandwidth. My CPU is really
    > fast (2 GHz) amd I dump the packets to the interface
    > in a tight loop in user space. However, I can only
    > reach around 400 Mbits/sec before the packets get
    > dropped. The queue discipline (qdisc) seems to be
    > responsible because the queue length (txqueuelen) is
    > only 100 by default, and the queue just cannot store
    > so many packets at once. I can eliminate the packet
    > drop by raising the queue length to somewhere like
    > 60000 but that is not practical because it uses too
    > much memory. It seems I need some delay between
    > sending packets but I cannot sleep for less than 10 ms
    > (1/Hz) in user space and 10 ms is too long.
    >
    > I am using raw socket bypassing the IP stack and my
    > NIC is the Intel Pro1000 (using the e1000.o driver).
    >
    > What is the best way to send raw ethernet packets,
    > reaching gigabit range withuut packet drop on Linux?
    > Thanks for any advice.

    Make sure the e1000 driver is tuned, try insmodding it with:
    TxDescriptors=1024 RxDescriptors=4096

    Also, in your user-space app, check the return code of your
    packet-sending call. That can let you know that the kernel
    dropped it, and that you need to re-send.

    How do you know you are dropping packets? (Ie, are you also
    reading on another machine?) Usually it's read that drops
    more packets than write.

    Good luck,
    Ben

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