GNU bug report logs - #73649
OpenMPI + mpi4py broken: rank=0

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Antero Mejr <mail <at> antr.me>
To: bug-guix <at> gnu.org
Subject: OpenMPI + mpi4py broken: rank=0
Date: Sun, 06 Oct 2024 01:01:33 +0000

Running this command:

guix shell python python-mpi4py openmpi -- mpirun -n 12 python3 \
-c "from mpi4py import MPI; comm = MPI.COMM_WORLD;
print(comm.Get_rank())"

should print the numbers 0-11. Instead it prints 0 11 times. The same
behavior occurs in a container or pure environment.

This breaks any code using mpi4py, because ranks >0 must be available
for multi-threaded code to work.

Message #8 received at 73649 <at> debbugs.gnu.org (full text, mbox):

From: Lars Bilke <lars.bilke <at> ufz.de>
To: mail <at> antr.me
Cc: 73649 <at> debbugs.gnu.org
Subject: Re: bug#73649: OpenMPI + mpi4py broken: rank=0
Date: Tue, 10 Dec 2024 14:03:44 +0100

The issue seems that openmpi is version 5.x but mpi4py is compiled against version 4.x. You can get a consistent version by using this flag: --with-input=openmpi=openmpi <at> 4.1.6.  I could fix the issue with this call:

guix shell python python-mpi4py openmpi \
  --with-input=openmpi=openmpi <at> 4.1.6 -- \
  mpirun -n 12 python3 ...

Message #11 received at 73649 <at> debbugs.gnu.org (full text, mbox):

From: Antero Mejr <mail <at> antr.me>
To: Lars Bilke <lars.bilke <at> ufz.de>
Cc: 73649 <at> debbugs.gnu.org
Subject: Re: bug#73649: OpenMPI + mpi4py broken: rank=0
Date: Wed, 11 Dec 2024 18:35:27 -0500

Lars Bilke <lars.bilke <at> ufz.de> writes:

> The issue seems that openmpi is version 5.x but mpi4py is compiled against
> version 4.x.

That does fix it, thanks. Maybe packages built against MPI 4.x should
be upgraded to the default MPI version, because the docs say:

"The Open MPI v5.0.x series shared libraries are ABI compatible with
Open MPI v4.0.x and v4.1.x, with a few exceptions for Fortran."

https://docs.open-mpi.org/en/v5.0.x/version-numbering.html

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