Fix MPI synchronization in real.exe #1600
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(cherry picked from commit 183600b)
This was referenced Dec 15, 2021
davegill
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…l#1600) TYPE: [bug fix] KEYWORDS: real.exe, MPI, bug fix SOURCE: Marc Honnorat (EXWEXs) DESCRIPTION OF CHANGES: Problem: The communicator `mpi_comm_allcompute`, created by subroutine `split_communicator` called by `init_modules(1)`, is not explicitly activated for the call to `wrf_dm_bcast_bytes( configbuf, nbytes )` in real.exe. On some platforms, this may prevent broadcast of namelist configuration (put in `configbuf` after the call to `get_config_as_buffer()`) across the MPI processes _before_ the call to `setup_physics_suite()`. An example of a problematic platform: a cluster of Intel Xeon E5-2650 v4 running on CentOS Linux release 7.6.1810, with Intel Parallel Studio XE (various versions, including 2018u3 and 2020u4) and Intel MPI Library (same version). Solution: The initialization step used in the WRF executable never triggers a failure as described in issue wrf-model#1267. This PR reuses the temporary MPI context switch from WRF code. ISSUE: Fixes wrf-model#1267 LIST OF MODIFIED FILES: M main/real_em.F TESTS CONDUCTED: 1. The modification systematically solves the problem on the noted cluster. 2. Jenkins tests are all passing. RELEASE NOTE: A fix for an MPI synchronization bug related to (not used) split communicators in the real program provides a solution to issue wrf-model#1267. For users that have had no troubles with the real program running MPI, this will have no impact.
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TYPE: [bug fix]
KEYWORDS: real.exe, MPI, bug fix
SOURCE: Marc Honnorat (EXWEXs)
DESCRIPTION OF CHANGES:
Problem:
The communicator
mpi_comm_allcompute, created by subroutinesplit_communicatorcalled byinit_modules(1),is not explicitly activated for the call to
wrf_dm_bcast_bytes( configbuf, nbytes )in real.exe. On some platforms,this may prevent broadcast of namelist configuration (put in
configbufafter the call toget_config_as_buffer())across the MPI processes before the call to
setup_physics_suite().An example of a problematic platform: a cluster of Intel Xeon E5-2650 v4 running on CentOS Linux release 7.6.1810,
with Intel Parallel Studio XE (various versions, including 2018u3 and 2020u4) and Intel MPI Library (same version).
Solution:
The initialization step used in the WRF executable never triggers a failure as described in issue #1267. This PR reuses
the temporary MPI context switch from WRF code.
ISSUE:
Fixes #1267
LIST OF MODIFIED FILES:
M main/real_em.F
TESTS CONDUCTED:
RELEASE NOTE: A fix for an MPI synchronization bug related to (not used) split communicators in the real program provides a solution to issue #1267. For users that have had no troubles with the real program running MPI, this will have no impact.