Intel® Math Kernel Library 11.3 Update 4 Developer Guide
This section summarizes typical usage models and available options for calling Intel MKL functions from multi-threaded applications. These recommendations apply to any multi-threading environments: OpenMP*, Intel® Threading Building Blocks, POSIX* threads, and others.
When used: Intel MKL internal threading interferes with application's own threading or may slow down the application.
Example: the application is threaded at top level, or the application runs concurrently with other applications.
Options:
Link statically or dynamically with the sequential library
Link with the Single Dynamic Library mkl_rt.so and select the sequential library using an environment variable or a function call:
Set MKL_THREADING_LAYER=sequential
Call mkl_set_threading_layer(MKL_THREADING_SEQUENTIAL)‡
When used: application threads are specialized for a particular computation.
Example: one thread solves equations on all cores but one, while another thread running on a single core updates a database.
Linking Options:
Link statically or dynamically with a threading library
Link with the Single Dynamic Library mkl_rt.so and select a threading library using an environment variable or a function call:
set MKL_THREADING_LAYER=intel or MKL_THREADING_LAYER=tbb
call mkl_set_threading_layer(MKL_THREADING_INTEL) or mkl_set_threading_layer(MKL_THREADING_TBB)
Other Options for OpenMP Threading:
Set the MKL_NUM_THREADS environment variable to a desired number of OpenMP threads for Intel MKL.
Set the MKL_DOMAIN_NUM_THREADS environment variable to a desired number of OpenMP threads for Intel MKL for a particular function domain.
Use if the application threads work with different Intel MKL function domains.
Call mkl_set_num_threads()
Use to globally set a desired number of OpenMP threads for Intel MKL at run time.
Call mkl_domain_set_num_threads().
Use if at some point application threads start working with different Intel MKL function domains.
Call mkl_set_num_threads_local().
Use to set the number of OpenMP threads for Intel MKL called from a particular thread.
If your application uses OpenMP* threading, you may need to provide additional settings:
Set the environment variable MKL_DYNAMIC=FALSE, or alternatively call mkl_set_dynamic(0), to prevent Intel MKL from dynamically reducing the number of OpenMP threads in nested parallel regions.
‡ For details of the mentioned functions, see the Support Functions section of the Intel MKL Developer Reference, available in the Intel Software Documentation Library.
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