Intel(R) - Computational and Systems Biology at MIT

6 Intel® Math Kernel Library User’s GuideWhereas the MKL_DOMAIN_NUM_THREADS environment variable enables you set severalvariables at once, for example, "MKL_BLAS=4,MKL_FFT=2", the corresponding functiondoes not take string syntax. So, to do the same with the function calls, you may need tomake 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 );Setting the Environment Variables for Threading ControlTo set the environment variables used for threading control, in the command shell in whichthe program is going to run, enter:export = for certain shells, such as bash.For example,export MKL_NUM_THREADS=4export MKL_DOMAIN_NUM_THREADS="MKL_ALL=1, MKL_BLAS=4"export MKL_DYNAMIC=FALSEFor other shells, such as csh or tcsh, enterset = .For example,set MKL_NUM_THREADS=4set MKL_DOMAIN_NUM_THREADS="MKL_ALL=1, MKL_BLAS=4"set MKL_DYNAMIC=FALSENote on FFT UsageIntroduction of additional threading control made it possible to optimize the commit stageof the FFT implementation and get rid of double data initialization. However, thisoptimization requires a change in the FFT usage. Suppose you create threads in theapplication yourself after initializing all FFT descriptors. In this case, threading is employedfor the parallel FFT computation only, the descriptors are released upon return from theparallel region, and each descriptor is used only within the corresponding thread. Startingwith Intel MKL 10.0, you must explicitly instruct the library before the commit stage towork on one thread. To do this, set MKL_NUM_THREADS=1 orMKL_DOMAIN_NUM_THREADS="MKL_FFT=1" or call the corresponding pair of servicefunctions. Otherwise, the actual number of threads may be different because theDftiCommitDescriptor function is not in a parallel region. See Example C-27a "UsingParallel Mode with Multiple Descriptors Initialized in One Thread" in the Intel MKLReference Manual.6-12