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SubjectRe: Network performance degradation from to
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

Andrew Morton wrote:
> On Fri, 16 Jun 2006 09:01:23 -0700
> Harry Edmon <> wrote:
>> I have a system with a strange network performance degradation from
>> to most recent kernels including 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
>> ( 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 kernel falls way
>> behind with the data ingestion. The 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 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:
Dept of Atmospheric Sciences FAX: 206-543-0308
University of Washington, Box 351640, Seattle, WA 98195-1640
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