Intel(R) - Computational and Systems Biology at MIT

6 Intel® Math Kernel Library User’s GuideUsing Additional Threading ControlIntel MKL 10.0 introduces new optional threading controls, that is, the environmentvariables and service functions. They behave similar to their OpenMP equivalents, but takeprecedence over them. By using these controls along with OpenMP variables, you canthread the part of the application that does not call Intel MKL and the library independentlyfrom each other.These controls enable you to specify the number of threads for Intel MKL independently ofthe OpenMP settings. Although Intel MKL may actually use the number of threads thatdiffers from the one suggested, the controls will also enable you to instruct the library totry using the suggested number in the event of undetectable threading behavior in theapplication calling the library.NOTE. Intel MKL does not always have a choice on the number ofthreads for certain reasons, such as system resources.Employing Intel MKL threading controls in your application is optional. If you do not usethem, the library will mainly behave the same way as Intel MKL 9.1 in what relates tothreading with the possible exception of a different default number of threads. See Note onFFT Usage for the usage differences.Table 6-2 lists the Intel MKL environment variables for threading control, their equivalentfunctions, and OMP counterparts:Table 6-2Intel® MKL environment variables for threading controlsEnvironment Variable Service Function CommentMKL_NUM_THREADS mkl_set_num_threads Suggests the number ofthreads to use.MKL_DOMAIN_NUM_THREADSmkl_domain_set_num_threadsSuggests the number ofthreads for a particularfunction domain.MKL_DYNAMIC mkl_set_dynamic Enables Intel MKL todynamically change thenumber of threads.Equivalent OMPEnvironmentVariableOMP_NUM_THREADSOMP_DYNAMIC6-8