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SubjectRe: Network performance degradation from 2.6.11.12 to 2.6.16.20
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.
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