Visible to Intel only — GUID: GUID-B530388E-B96C-48A2-A498-DCBA4E6CFEDC
Visible to Intel only — GUID: GUID-B530388E-B96C-48A2-A498-DCBA4E6CFEDC
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 |
Fourier Transform Functions |
MKL_DOMAIN_LAPACK |
LAPACK Routines |
MKL_DOMAIN_VML |
Vector Mathematics (VM) |
MKL_DOMAIN_PARDISO |
Intel® oneAPI Math Kernel Library (oneMKL) PARDISO, a direct sparse solver based on Parallel Direct Sparse Solver (PARDISO*) |
For example, you could set the MKL_DOMAIN_NUM_THREADSenvironment variable to any of the following string variants, in this case, defining three specific domain variables internal to Intel® oneAPI Math Kernel Library (oneMKL):
MKL_DOMAIN_NUM_THREADS="MKL_DOMAIN_ALL=2, MKL_DOMAIN_BLAS=1, MKL_DOMAIN_FFT=4"
MKL_DOMAIN_NUM_THREADS="MKL_DOMAIN_ALL 2 : MKL_DOMAIN_BLAS 1 : MKL_DOMAIN_FFT 4"
MKL_DOMAIN_NUM_THREADS="MKL_DOMAIN_ALL=2 : MKL_DOMAIN_BLAS=1 : MKL_DOMAIN_FFT=4"
MKL_DOMAIN_NUM_THREADS="MKL_DOMAIN_ALL=2; MKL_DOMAIN_BLAS=1; MKL_DOMAIN_FFT=4"
MKL_DOMAIN_NUM_THREADS="MKL_DOMAIN_ALL=2 MKL_DOMAIN_BLAS 1, MKL_DOMAIN_FFT 4"
MKL_DOMAIN_NUM_THREADS="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® oneAPI Math Kernel Library (oneMKL) threading control functions, can be found in themkl.h header file.
This table 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® oneAPI Math Kernel Library (oneMKL) should try four OpenMP threads. The actual number of threads may be still different because of theMKL_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® oneAPI Math Kernel Library (oneMKL) 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® oneAPI Math Kernel Library (oneMKL). |
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 );