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Lassen: Work-Around MPI Allgatherv #2874

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Feb 24, 2022
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17 changes: 17 additions & 0 deletions Docs/source/install/hpc/lassen.rst
Original file line number Diff line number Diff line change
Expand Up @@ -88,3 +88,20 @@ regime), the following set of parameters provided good performance:
node)

* **Two `128x128x128` grids per GPU**, or **one `128x128x256` grid per GPU**.


.. _building-lassen-issues:

Known System Issues
-------------------

.. warning::

Feb 17th, 2022 (INC0278922):
The implementation of AllGatherv in IBM's MPI optimization library "libcollectives" is broken and leads to HDF5 crashes for multi-node runs.

Our batch script templates above `apply this work-around <https://github.com/ECP-WarpX/WarpX/pull/2874>`__ *before* the call to ``jsrun``, which avoids the broken routines from IBM and trades them for an OpenMPI implementation of collectives:

.. code-block:: bash

export OMPI_MCA_coll_ibm_skip_allgatherv=true
6 changes: 5 additions & 1 deletion Tools/machines/lassen-llnl/lassen.bsub
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@@ -1,6 +1,6 @@
#!/bin/bash

# Copyright 2020 Axel Huebl
# Copyright 2020-2022 Axel Huebl
#
# This file is part of WarpX.
#
Expand All @@ -22,5 +22,9 @@
# https://github.com/open-mpi/ompi/issues/7795
export OMPI_MCA_io=ompio

# Work-around for broken IBM "libcollectives" MPI_Allgatherv
# https://github.com/ECP-WarpX/WarpX/pull/2874
export OMPI_MCA_coll_ibm_skip_allgatherv=true

export OMP_NUM_THREADS=1
jsrun -r 4 -a 1 -g 1 -c 7 -l GPU-CPU -d packed -b rs -M "-gpu" <path/to/executable> <input file> > output.txt