To improve performance of cluster applications, it is critical for

Intel® oneAPI Math Kernel Library

to use the optimal number of threads, as well as the correct thread affinity. Usually, the optimal number is the number of available cores per node divided by the number of MPI processes per node. You can set the number of threads using one of the available methods, described inTechniques to Set the Number of Threads.

If the number of threads is not set,

Intel® oneAPI Math Kernel Library

checks whether it runs under MPI provided by the Intel® MPI Library. If this is true, the following environment variables define

Intel® oneAPI Math Kernel Library

threading behavior:

The threading behavior depends on the value of

I_MPI_THREAD_LEVEL

as follows:

0 or undefined.
Intel® oneAPI Math Kernel Library
considers that thread support level of Intel MPI Library is
MPI_THREAD_SINGLE
and defaults to sequential execution.
1, 2, or 3.
This value determines
Intel® oneAPI Math Kernel Library
conclusion of the thread support level:
1 -
MPI_THREAD_FUNNELED
2 -
MPI_THREAD_SERIALIZED
3 -
MPI_THREAD_MULTIPLE
In all these cases,
Intel® oneAPI Math Kernel Library
determines the number of MPI processes per node using the other environment variables listed and defaults to the number of threads equal to the number of available cores per node divided by the number of MPI processes per node.