SMP and Network Connections

Joseph Mack mack.joseph at
Thu Apr 17 10:45:51 EDT 2003

Douglas Eadline wrote:
> Just posted some more SMP tests on
> This time, I tested the interconnects and asked the
> question "What if a dual SMP used two Ethernet connections
> instead of one?" Seems to help! Take a look at:

Thanks for your work and write up. 

I did some performance tests a few years ago on a router,
using multiple copies of netpipe through a single interface 
to a set of nodes, to determine the effect of multiple streams
on throughput on the router (this was 100Mbps ethernet).

I found that as I increased the number of nodes connecting
to the router, that the throughput increased, rising above
100Mbps (when I totalled the throughput from each netpipe

Looking at the netpipe code I saw that netpipe waits for a
quiet time on the network before entering the next round of
the test. Thus for 4 connections, if each instance of
netpipe waited for a quiet time to run the test on the next
packet size, I could (in principle) get the result of 4 connections
of 100Mpbs for a total of 400Mpbs. 

I contacted the netpipe author, who sent me a preliminary version
of a multi-netpipe, where multiple connections are synchronised
and stepped through the range of packet sizes together. He
said that it wasn't ready to use and I didn't have time to 
work on it myself. I never solved the multiple connection 
problem and wound up doing tests with a single connection.

Do you know if this problem is affecting your measurements?

(The report is at


Joseph Mack PhD, Senior Systems Engineer, SAIC contractor 
to the National Environmental Supercomputer Center, 
ph# 919-541-0007, RTP, NC, USA. mailto:mack.joseph at
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