Intel® oneAPI Math Kernel Library (oneMKL)

is extensively parallelized. SeeOpenMP* Threaded Functions and Problems and Functions Threaded with Intel® Threading Building Blocks for lists of threaded functions and problems that can be threaded.

Intel® oneAPI Math Kernel Library

is

thread-safe

, which means that all

Intel® oneAPI Math Kernel Library

functions (except the LAPACK deprecated routine

?lacon)

work correctly during simultaneous execution by multiple threads. In particular, any chunk of threaded

Intel® oneAPI Math Kernel Library

code provides access for multiple threads to the same shared data, while permitting only one thread at any given time to access a shared piece of data. Therefore, you can call

Intel® oneAPI Math Kernel Library

from multiple threads and not worry about the function instances interfering with each other.

If you are using OpenMP* threading technology,

you can use the environment variable

OMP_NUM_THREADS

to specify the number of threads or the equivalent OpenMP run-time function calls.

Intel® oneAPI Math Kernel Library

also offers variables that are independent of OpenMP, such as

MKL_NUM_THREADS

, and equivalent

Intel® oneAPI Math Kernel Library

functions for thread management. The

Intel® oneAPI Math Kernel Library

variables are always inspected first, then the OpenMP variables are examined, and if neither is used, the OpenMP software chooses the default number of threads.

By default,

Intel® oneAPI Math Kernel Library

uses the number of

OpenMP

threads equal to the number of physical cores on the system.

If you are using the Intel TBB threading technology, the OpenMP threading controls, such as the

OMP_NUM_THREADS

environment variable or

MKL_NUM_THREADS

function, have no effect. Use the Intel TBB application programming interface to control the number of threads.

To achieve higher performance, set the number of threads to the number of processors or physical cores, as summarized in Techniques to Set the Number of Threads.