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Subject: [OMPI users] unsubscribe
From: Lane, William (William.Lane_at_[hidden])
Date: 2011-09-19 04:50:34


please unsubscribe me from this maillist.

Thank you,

-Bill Lane
________________________________
From: users-bounces_at_[hidden] [users-bounces_at_[hidden]] on behalf of Ole Nielsen [ole.moller.nielsen_at_[hidden]]
Sent: Monday, September 19, 2011 1:39 AM
To: users_at_[hidden]
Subject: Re: [OMPI users] MPI hangs on multiple nodes

Further to the posting below, I can report that the test program (attached - this time correctly) is chewing up CPU time on both compute nodes for as long as I care to let it continue.
It would appear that MPI_Receive which is the next command after the print statements in the test program.

Has anyone else seen this behavior or can anyone give me a hint on how to troubleshoot.
Cheers and thanks
Ole Nielsen

Output:
nielso_at_alamba:~/sandpit/pypar/source$ mpirun --hostfile /etc/mpihosts --host node17,node18 --npernode 2 a.out
Number of processes = 4
Test repeated 3 times for reliability
I am process 2 on node node18
P2: Waiting to receive from to P1
I am process 0 on node node17
Run 1 of 3
P0: Sending to P1
I am process 1 on node node17
P1: Waiting to receive from to P0
I am process 3 on node node18
P3: Waiting to receive from to P2
P0: Waiting to receive from P3
P1: Sending to to P2
P1: Waiting to receive from to P0
P2: Sending to to P3
P0: Received from to P3
Run 2 of 3
P0: Sending to P1
P3: Sending to to P0
P3: Waiting to receive from to P2
P2: Waiting to receive from to P1
P1: Sending to to P2
P0: Waiting to receive from P3

On Mon, Sep 19, 2011 at 11:04 AM, Ole Nielsen <ole.moller.nielsen_at_[hidden]<mailto:ole.moller.nielsen_at_[hidden]>> wrote:

Hi all

We have been using OpenMPI for many years with Ubuntu on our 20-node cluster. Each node has 2 quad cores, so we usually run up to 8 processes on each node up to a maximum of 160 processes.

However, we just upgraded the cluster to Ubuntu 11.04 with Open MPI 1.4.3 and and have come across a strange behavior where mpi programs run perfectly well when confined to one node but hangs during communication across multiple nodes. We have no idea why and would like some help in debugging this. A small MPI test program is attached and typical output shown below.

Hope someone can help us
Cheers and thanks
Ole Nielsen

-------------------- Test output across two nodes (This one hangs) --------------------------
nielso_at_alamba:~/sandpit/pypar/source$ mpirun --hostfile /etc/mpihosts --host node17,node18 --npernode 2 a.out
Number of processes = 4
Test repeated 3 times for reliability
I am process 1 on node node17
P1: Waiting to receive from to P0
I am process 0 on node node17
Run 1 of 3
P0: Sending to P1
I am process 2 on node node18
P2: Waiting to receive from to P1
I am process 3 on node node18
P3: Waiting to receive from to P2
P1: Sending to to P2

-------------------- Test output within one node (This one is OK) --------------------------
nielso_at_alamba:~/sandpit/pypar/source$ mpirun --hostfile /etc/mpihosts --host node17 --npernode 4 a.out
Number of processes = 4
Test repeated 3 times for reliability
I am process 2 on node node17
P2: Waiting to receive from to P1
I am process 0 on node node17
Run 1 of 3
P0: Sending to P1
I am process 1 on node node17
P1: Waiting to receive from to P0
I am process 3 on node node17
P3: Waiting to receive from to P2
P1: Sending to to P2
P2: Sending to to P3
P1: Waiting to receive from to P0
P2: Waiting to receive from to P1
P3: Sending to to P0
P0: Received from to P3
Run 2 of 3
P0: Sending to P1
P3: Waiting to receive from to P2
P1: Sending to to P2
P2: Sending to to P3
P1: Waiting to receive from to P0
P3: Sending to to P0
P2: Waiting to receive from to P1
P0: Received from to P3
Run 3 of 3
P0: Sending to P1
P3: Waiting to receive from to P2
P1: Sending to to P2
P2: Sending to to P3
P1: Done
P2: Done
P3: Sending to to P0
P0: Received from to P3
P0: Done
P3: Done

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