Intel(R) Math Kernel Library for Linux* OS User's Guide

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9 Intel® Math Kernel Library User’s Guide is one of ScaLAPACK or Cluster FFT libraries for theappropriate architecture, which are listed in Table 3-6, Table 3-7, or Table 3-8. Forexample, for IA-32 architecture, it is one of -lmkl_scalapack_core or-lmkl_cdft_core. is the BLACS library corresponding to your architecture, programminginterface (LP64 or ILP64), and MPI version. These libraries are listed in Table 3-6,Table 3-7, or Table 3-8. For example, for the IA-32 architecture, choose one of-lmkl_blacs, -lmkl_blacs_intelmpi, or -lmkl_blacs_openmpi, depending onthe MPI version you use; in particular, for Intel MPI 3.x, choose-lmkl_blacs_intelmpi. is forScaLAPACK, and for Cluster FFTs. are processor optimized kernels, threading library, andsystem library for threading support, linked as described in section Listing Libraries ona Link Line. are the LAPACK library and .grouping symbols -Wl,--start-group and -Wl,--end-group are required for staticlinking. corresponds to the MPI version. For instance, for Intel MPI3.x, use .For example, if you are using Intel MPI 3.x and want to statically use the LP64 interfacewith ScaLAPACK and have only one MPI process per core (and thus do not employthreading), specify the following linker options:-L$MKLPATH -I$MKLINCLUDE -Wl,--start-group$MKLPATH/libmkl_scalapack_lp64.a $MKLPATH/libmkl_blacs_intelmpi_lp64.a$MKLPATH/libmkl_intel_lp64.a $MKLPATH/libmkl_sequential.a$MKLPATH/libmkl_core.a -static_mpi -Wl,--end-group -lpthread –lmFor more examples, see Examples for Linking with ScaLAPACK and Cluster FFT.TIP. Use the Web-based Linking Advisor to quickly choose theappropriate set of , , and .For information on linking with Intel® MKL libraries, see Linking Your Application with theIntel® Math Kernel Library.9-2
Setting the Number of ThreadsWorking with the Intel® Math Kernel Library Cluster Software 9The OpenMP* software responds to the environment variable OMP_NUM_THREADS. Intel MKLalso has other mechanisms to set the number of threads, such as the MKL_NUM_THREADSor MKL_DOMAIN_NUM_THREADS environment variables (see Using Additional ThreadingControl).Make sure that the relevant environment variables have the same and correct values on allthe nodes. Intel MKL versions 10.0 and higher no longer set the default number of threadsto one, but depend on the OpenMP libraries used with the compiler to set the defaultnumber. For the threading layer based on the Intel® compiler (libmkl_intel_thread.a),this value is the number of CPUs according to the OS.CAUTION. Avoid over-prescribing the number of threads, which mayoccur, for instance, when the number of MPI ranks per node and thenumber of threads per node are both greater than one. The product ofMPI ranks per node and the number of threads per node should notexceed the number of physical cores per node.The best way to set an environment variable, such as OMP_NUM_THREADS, is your loginenvironment. Remember that changing this value on the head node and then doing yourrun, as you do on a shared-memory (SMP) system, does not change the variable on all thenodes because mpirun starts a fresh default shell on all of the nodes. To change thenumber of threads on all the nodes, in .bashrc, add a line at the top, as follows:OMP_NUM_THREADS=1; export OMP_NUM_THREADSYou can run multiple CPUs per node using MPICH. To do this, build MPICH to enablemultiple CPUs per node. Be aware that certain MPICH applications may fail to workperfectly in a threaded environment (see the Known Limitations section in the ReleaseNotes). If you encounter problems with MPICH and setting of the number of threads isgreater than one, first try setting the number of threads to one and see whether theproblem persists.Using Shared LibrariesAll needed shared libraries must be visible on all the nodes at run time. To achieve this,point these libraries by the LD_LIBRARY_PATH environment variable in the .bashrc file.If Intel MKL is installed only on one node, link statically when building your Intel MKLapplications rather than use shared libraries.The Intel® compilers or GNU compilers can be used to compile a program that uses IntelMKL. However, make sure that the MPI implementation and compiler match up correctly.9-3
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Intel(R) Math Kernel Library for Linux* OS User's Guide

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