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    SubjectRe: Network performance degradation from 2.6.11.12 to 2.6.16.20
    I assume you are talking about using TCP_NODELAY as a socket option within the 
    LDM software. I could give that a try.

    There is a lot of traffic on this node, on the order of 2000 packets in and out
    per second, so the tcpdump output will grow pretty fast. How long a tcpdump
    would be useful, and what options would you suggest?

    I should also note that my network interfaces are Intel, using the latest e1000
    driver.


    Andrew Morton wrote:
    > On Fri, 16 Jun 2006 09:01:23 -0700
    > Harry Edmon <harry@atmos.washington.edu> wrote:
    >
    >> I have a system with a strange network performance degradation from
    >> 2.6.11.12 to most recent kernels including 2.6.16.20 and 2.6.17-rc6.
    >> The system is has Dual single core Xeons with hyperthreading on. The
    >> application is the LDM system from UCAR/Unidata
    >> (http://www.unidata.ucar.edu/software/ldm). This system requests
    >> weather data from a variety of systems using RPC calls over a reserved
    >> TCP port (388), puts them into a memory mapped queue file, and then
    >> sends the data out to a variety of downstream requesting systems, again
    >> using RPC calls. When the load is heavy, the 2.6.16.20 kernel falls way
    >> behind with the data ingestion. The 2.6.11.12 kernel does not. I have
    >> tried an experiment with a 2.6.17-rc6 system where it just does the
    >> ingestion, and not the downstream distribution, and it is able to keep
    >> up. I would really appreciate any pointers as to where the problem may
    >> be and how to diagnose it. I have attached the config files from both
    >> kernels and the sysctl.conf file I am using. I have also included the
    >> output from "netstat -s" on the 2.6.16.20 system during a time when it
    >> was having problems.
    >>
    >
    > (added netdev)
    >
    > A quick grep indicates that it isn't using TCP_NODELAY - we've had problems
    > with that in the past.
    >
    > Perhaps a tcpdump of the net traffic will help to determine what's going on.


    --
    Dr. Harry Edmon E-MAIL: harry@atmos.washington.edu
    206-543-0547 harry@u.washington.edu
    Dept of Atmospheric Sciences FAX: 206-543-0308
    University of Washington, Box 351640, Seattle, WA 98195-1640
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