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Subject: Re: [OMPI users] Running Open MPI on Ethernet
From: John Hearns (john.hearns_at_[hidden])
Date: 2008-08-08 08:25:20

On Fri, 2008-08-08 at 20:11 +0800, Rayne wrote:
> Hi all,
> I'm running openmpi-1.2.6, and my computer is connected to a Ethernet network. I have no experience in setting up a network that supports parallel computing using MPI before, nor do I know much about networking. So please excuse me if my questions seem too simple or silly.

> Hello... 0 of 3 processors
> Hello... 1 of 3 processors
> Hello... 2 of 3 processors
> 0 Calculated total: 3
> 0 Reduced total: 3
> together with the warning message about OpenIB and UDAPL, which after some Googling, I was able to resolve using "-mca btl ^openib,udapl".
> I was trying to see if my MPI program is really running on the Ethernet network, so I deactivated the network, but the program still works. Then I unplugged the network cable and still the program works. Then I ran Wireshark, which is a kind of packet sniffer program, and ran the MPI program again to see if the Send/Receive functions work right, as I thought if the program is sending/receiving the variable i, something should show up in Wireshark. However, no packets are captured by Wireshark.
> Can someone help me understand what is going on here, as it seems like the program is working when it shouldn't?

Your code is probably running just on your local machine.
Run 'top' on your machine in another window, and set your code to loop
several times and you will see what I mean.

If you have other machines on the network, you have to configure them
such that you can start remote processes on them.
When you use "mpirun" to launch your MPI code you need to give the names
of those machines as a parameter to mpirun - it is known as a "machines

John Hearns