.. _Chap:InputsComputeBackends: Compute Backends ================ The following inputs must be preceded by ``amrex.`` and determine runtime options of CPU or GPU compute implementations. +------------------------+-----------------------------------------------------------------------+-------------+------------+ | Parameter | Description | Type | Default | +========================+=======================================================================+=============+============+ | ``omp_threads`` | If OpenMP is enabled, this can be used to set the default number of | String | ``system`` | | | threads. The special value ``nosmt`` can be used to avoid using | or Int | | | | threads for virtual cores (aka Hyperthreading or SMT), as is default | | | | | in OpenMP, and instead only spawns threads equal to the number of | | | | | physical cores in the system. | | | | | For the values ``system`` and ``nosmt``, the environment variable | | | | | ``OMP_NUM_THREADS`` takes precedence. For Integer values, | | | | | ``OMP_NUM_THREADS`` is ignored. | | | +------------------------+-----------------------------------------------------------------------+-------------+------------+ For GPU-specific parameters, see also the :ref:`GPU chapter `.