Re: Network performance degradation from 2.6.11.12 to 2.6.16.20

[Harry Edmon <harry@atmos.washington.edu>]

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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