OpenMP parallelization

OpenGeoSys supports shared memory parallelization (multi threading) to some extent: by default OpenGeoSys is built with OpenMP support and OpenMP-enabled linear solvers will automatically make use of it.

The number of threads a linear solver uses can be controlled with the environment variable OMP_NUM_THREADS.

Note:

• Some linear solvers and some preconditioners from the Eigen library run with a single thread only, see here.
• For Eigen’s CG solver, multi-threading can be exploited using both triangular matrices (see here. This can be set in OGS using <triangular_matrix>LowerUpper</triangular_matrix> as linear solver option.
• When using distributed memory parallelization (MPI) it might not make sense to use OpenMP at the same time: the different threads might compete for the same CPU resources.
• There is an interference between the Intel MKL and OpenMP parallelization: If you use OGS together with the former, you might break the latter. In that case you might want to change the OGS_EIGEN_PARALLEL_BACKEND.

In addition, the assembly of some processes in OGS can be run OpenMP-parallelized when setting the environment variable OGS_ASM_THREADS to the number of threads to be used. At the moment (2024-09-09) that’s supported by the HydroMechanics, TH2M, ThermoRichardsMechanics, and ThermoRichardsFlow processes.