The MKL_DOMAIN_NUM_THREADS environment variable suggests the number of 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_ALL | MKL_BLAS | MKL_FFT | MKL_VML
<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, MKL_BLAS indicates the BLAS function domain, MKL_FFT indicates non-cluster FFTs, and MKL_VML indicates the Vector Mathematics Library.
For example,
MKL_ALL 2 : MKL_BLAS 1 : MKL_FFT 4
MKL_ALL=2 : MKL_BLAS=1 : MKL_FFT=4
MKL_ALL=2, MKL_BLAS=1, MKL_FFT=4
MKL_ALL=2; MKL_BLAS=1; MKL_FFT=4
MKL_ALL = 2 MKL_BLAS 1 , MKL_FFT 4
MKL_ALL,2: MKL_BLAS 1, MKL_FFT,4 .
The global variables MKL_ALL, MKL_BLAS, MKL_FFT, and MKL_VML, 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_ALL=4 |
All parts of Intel MKL should try four 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_ALL=1, MKL_BLAS=4 |
All parts of Intel MKL should try one thread, except for BLAS, which is suggested to try four threads. |
|
MKL_VML=2 |
VML should try two 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_BLAS=4"
value of
MKL_DOMAIN_NUM_THREADS
suggests trying four threads for BLAS, regardless of later setting
MKL_NUM_THREADS,
and a function call "mkl_domain_set_num_threads ( 4, MKL_BLAS );"
suggests the same, regardless of later calls to
mkl_set_num_threads().
However, a function call with input "MKL_ALL", such as "mkl_domain_set_num_threads (4, MKL_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_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_BLAS=4,MKL_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_BLAS );
mkl_domain_set_num_threads ( 2, MKL_FFT );