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    SubjectRe: BUG: Slowdown on 3000 socket-machines tracked down
    Ben Greear wrote:
    > Christian Schmid wrote:
    >> Hello.
    >> After weeks of work, I can now give a detailed report about the bug
    >> and when it appears:
    >> Attached is another traffic-image. This one is with 2.6.10 and a 3/1
    >> split, preemtive kernel, so all defaults.
    > What are the units on your graph. You say "MB" several places, but
    > do you mean Mb (ie, Mega-bit) instead?

    The unit on this graph is kilobytes. So 80000 there means 80 megabytes per second.

    > I have a tool that can also generate TCP traffic on a large number of
    > sockets. If I can understand what you are trying to do, I may be able
    > to reproduce the problem. My biggest machine at present has only
    > 2GB of RAM, however...not sure if that matters or not.

    It should not matter. Low-memory is both just 1 GB if you have default 32 bit with 3/1 split.

    > Are you sending traffic in only one direction, or more of a full-duplex
    > configuration?

    Its a full-duplex. Its a download-service with 3000 downloaders all over the world.

    > Is each socket running the same bandwidth?

    No. It ranges from 3 kb/sec to 100 kb/sec. 100 kb/sec is the limit because of the send-buffer limits.

    > What is this bandwidth?

    1000 MBit

    > Are you setting the send & rcv buffers in the socket creation
    > code? (To what values if so?)

    Yes. send-buffer to 64 kbytes and receive buffer to 16 kbytes.

    > How many bytes are you sending with each call to write()/sendto() whatever?

    I am using sendfile-call every 100 ms per socket with the poll-api. So basically around 40 kb per round.

    > Is there any significant latency between your sender and receiver machine?
    > If so, how much?

    3000 different downloaders, 3000 different locations, 3000 different machines ;)

    > What is the physical transport...GigE? 1500 MTU?



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