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Subject: Re: [OMPI users] mpi job is blocked
From: jody (jody.xha_at_[hidden])
Date: 2012-09-25 03:43:09

Hi Richard

When a collective call hangs, this usually means that one (or more)
processes did not reach this command.
Are you sure that all processes reach the allreduce statement?

If something like this happens to me, i insert print statements just
before the MPI-call so i can see which processes made
it to this point and which ones did not.

Hope this helps a bit

On Tue, Sep 25, 2012 at 8:20 AM, Richard <codemonkee_at_[hidden]> wrote:
> I have 3 computers with the same Linux system. I have setup the mpi cluster
> based on ssh connection.
> I have tested a very simple mpi program, it works on the cluster.
> To make my story clear, I name the three computer as A, B and C.
> 1) If I run the job with 2 processes on A and B, it works.
> 2) if I run the job with 3 processes on A, B and C, it is blocked.
> 3) if I run the job with 2 processes on A and C, it works.
> 4) If I run the job with all the 3 processes on A, it works.
> Using gdb I found the line at which it is blocked, it is here
> #7 0x00002ad8a283043e in PMPI_Allreduce (sendbuf=0x7fff09c7c578,
> recvbuf=0x7fff09c7c570, count=1, datatype=0x627180, op=0x627780,
> comm=0x627380)
> at pallreduce.c:105
> 105 err = comm->c_coll.coll_allreduce(sendbuf, recvbuf, count,
> It seems that there is a communication problem between some computers. But
> the above series of test cannot tell me what
> exactly it is. Can anyone help me? thanks.
> Richard
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