MKL_DOMAIN_NUM_THREADS

The MKL_DOMAIN_NUM_THREADS environment variable suggests the number of OpenMP threads for a particular function domain.

MKL_DOMAIN_NUM_THREADS accepts a string value <MKL-env-string>, which must have the following format:

<MKL-env-string> ::= <MKL-domain-env-string> { <delimiter><MKL-domain-env-string> }

<delimiter> ::= [ <space-symbol>* ] ( <space-symbol> | <comma-symbol> | <semicolon-symbol> | <colon-symbol>) [ <space-symbol>* ]

<MKL-domain-env-string> ::= <MKL-domain-env-name><uses><number-of-threads>

<MKL-domain-env-name> ::= MKL_DOMAIN_ALL | MKL_DOMAIN_BLAS | MKL_DOMAIN_FFT | MKL_DOMAIN_VML | MKL_DOMAIN_PARDISO

<uses> ::= [ <space-symbol>* ] ( <space-symbol> | <equality-sign> | <comma-symbol>) [ <space-symbol>* ]

<number-of-threads> ::= <positive-number>

<positive-number> ::= <decimal-positive-number> | <octal-number> | <hexadecimal-number>

In the syntax above, values of <MKL-domain-env-name> indicate function domains as follows:

MKL_DOMAIN_ALL

All function domains

MKL_DOMAIN_BLAS

BLAS Routines

MKL_DOMAIN_FFT

non-cluster Fourier Transform Functions

MKL_DOMAIN_VML

Vector Mathematics (VM)

MKL_DOMAIN_PARDISO

Intel MKL PARDISO, a direct sparse solver based on Parallel Direct Sparse Solver (PARDISO*)

For example,

MKL_DOMAIN_ALL 2 : MKL_DOMAIN_BLAS 1 : MKL_DOMAIN_FFT 4

MKL_DOMAIN_ALL=2 : MKL_DOMAIN_BLAS=1 : MKL_DOMAIN_FFT=4

MKL_DOMAIN_ALL=2,  MKL_DOMAIN_BLAS=1,  MKL_DOMAIN_FFT=4

MKL_DOMAIN_ALL=2;  MKL_DOMAIN_BLAS=1;  MKL_DOMAIN_FFT=4

MKL_DOMAIN_ALL  = 2  MKL_DOMAIN_BLAS 1 ,  MKL_DOMAIN_FFT  4

MKL_DOMAIN_ALL,2: MKL_DOMAIN_BLAS 1, MKL_DOMAIN_FFT,4 .

The global variables MKL_DOMAIN_ALL, MKL_DOMAIN_BLAS, MKL_DOMAIN_FFT,MKL_DOMAIN_VML, and MKL_DOMAIN_PARDISO, as well as the interface for the Intel MKL threading control functions, can be found in the mkl.h header file.

The table below illustrates how values of MKL_DOMAIN_NUM_THREADS are interpreted.

Value of MKL_DOMAIN_NUM_THREADS

Interpretation

MKL_DOMAIN_ALL=4

All parts of Intel MKL should try four OpenMP threads. The actual number of threads may be still different because of the MKL_DYNAMIC setting or system resource issues. The setting is equivalent to MKL_NUM_THREADS = 4.

MKL_DOMAIN_ALL=1, MKL_DOMAIN_BLAS=4

All parts of Intel MKL should try one OpenMP thread, except for BLAS, which is suggested to try four threads.

MKL_DOMAIN_VML=2

VM should try two OpenMP threads. The setting affects no other part of Intel MKL.

Be aware that the domain-specific settings take precedence over the overall ones. For example, the "MKL_DOMAIN_BLAS=4" value of MKL_DOMAIN_NUM_THREADS suggests trying four OpenMP threads for BLAS, regardless of later setting MKL_NUM_THREADS, and a function call "mkl_domain_set_num_threads ( 4, MKL_DOMAIN_BLAS );" suggests the same, regardless of later calls to mkl_set_num_threads().
However, a function call with input "MKL_DOMAIN_ALL", such as "mkl_domain_set_num_threads (4, MKL_DOMAIN_ALL);" is equivalent to "mkl_set_num_threads(4)", and thus it will be overwritten by later calls to mkl_set_num_threads. Similarly, the environment setting of MKL_DOMAIN_NUM_THREADS with "MKL_DOMAIN_ALL=4" will be overwritten with MKL_NUM_THREADS = 2.

Whereas the MKL_DOMAIN_NUM_THREADS environment variable enables you set several variables at once, for example, "MKL_DOMAIN_BLAS=4,MKL_DOMAIN_FFT=2", the corresponding function does not take string syntax. So, to do the same with the function calls, you may need to make several calls, which in this example are as follows:

mkl_domain_set_num_threads ( 4, MKL_DOMAIN_BLAS );

mkl_domain_set_num_threads ( 2, MKL_DOMAIN_FFT );

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