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Allow oversubscribing OpenMP threads.

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There is a strange interaction when using MPI and OpenMP on some
hardware/MPI implementations. I a serial run omp_get_num_procs() would
return the number of processors but when started under mpirun it would
always return 1.

With this we now allow users to use any amount of threads.
This commit is contained in:
Markus Blatt 2023-06-14 11:34:29 +02:00
parent ae1f319c10
commit 2906d7157d
2 changed files with 12 additions and 7 deletions
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5
opm/simulators/flow/FlowMainEbos.hpp
View File

@ -387,7 +387,10 @@ void handleExtraConvergenceOutput(SimulatorReport& report,
if (requested_threads > 0)
threads = requested_threads;
omp_set_num_threads(std::min(threads, omp_get_num_procs()));
// We are not limiting this to the number of processes
// reported by OpenMP as on some hardware (and some OpenMPI
// versions) this will be 1 when run with mpirun
omp_set_num_threads(threads);
}
#endif

14
opm/simulators/flow/Main.hpp
View File

@ -670,15 +670,17 @@ private:
// This function is called before the parallel OpenMP stuff gets initialized.
// That initialization happends after the deck is read and we want this message.
// Hence we duplicate the code of setupParallelism to get the number of threads.
if (std::getenv("OMP_NUM_THREADS"))
if (std::getenv("OMP_NUM_THREADS")) {
threads = omp_get_max_threads();
else
threads = std::min(2, omp_get_max_threads());
}
else {
threads = 2;
const int input_threads = EWOMS_GET_PARAM(TypeTag, int, ThreadsPerProcess);
const int input_threads = EWOMS_GET_PARAM(TypeTag, int, ThreadsPerProcess);
if (input_threads > 0)
threads = std::min(input_threads, omp_get_max_threads());
if (input_threads > 0)
threads = input_threads;
}
#endif
return threads;