Overview

With the added support for the Intel® Xeon Phi™ coprocessor in the lntel® MPI Library product, we've introduced a few new environment variables to help ease running MPI jobs on the new architecture. For full details on how to launch an Intel MPI Library job on a cluster containing Intel Xeon Phi coprocessor cards, check out this article.

Here, we discuss two specific methods that help in cases of an NFS-shared environment across the Xeon host and the Xeon Phi coprocessor card.

For the examples below, we assume a couple of things:

• The $HOME directory of each user (e.g. /home/user) is NFS-shared on the host and coprocessor. This will work for any other NFS-shared location where the executables are built
• We're using the Intel MPI wrapper scripts for the Intel® C Compilers (mpiicc). Feel free to replace with desired compiler (e.g. mpiifort for the Intel® Fortran Compiler).
• Finally, we've created an MPI hosts file that contains the hostnames of the Xeon Phi coprocessor cards:

  [user@host] $ cat mpi_hosts
  node0
  node0-mic0
  node1
  node1-mic0

Saving all Intel Xeon Phi coprocessor executables in a sub-directory

1. First create your executables which will be run on the Xeon hosts:

[user@host] $ mpiicc test.c –o test.exe

2. Now create a special directory where all Xeon Phi executables will live and populate it:

[user@host] $ mkdir MIC
[user@host] $ mpiicc –mmic test.c –o ./MIC/test.exe

3. Finally, launch your application. The trick here is to set the I_MPI_MIC_PREFIX environment variable. This will automatically add a prefix (e.g. ./MIC) to the executable when the mpirun script runs the MPI job on the Xeon Phi coprocessor cards.

[user@ host] $ export I_MPI_MIC=enable
[user@host] $ export I_MPI_MIC_PREFIX=./MIC/
[user@host] $ mpirun –f mpi_hosts –perhost 1 –n 2 test.exe
Hello world: rank 0 of 2 running on node0
Hello world: rank 1 of 2 running on node0-mic0

Using a Xeon Phi-specific extension for your Xeon Phi-specific executables

Step 1. is the same as the previous case.

2. Instead of creating a new directory, attach an extension to the Xeon Phi coprocessor executables during creation:

[user@host] $ mpiicc –mmic test.c –o test.exe.mic

3. Again, simply launch your application. The trick here is to set the I_MPI_MIC_POSTFIX environment variable. This will automatically attach the specified postfix (e.g. .mic) to the executable when the mpirun script runs the MPI job on the Xeon Phi coprocessor cards.

[user@ host] $ export I_MPI_MIC=enable
[user@host] $ export I_MPI_MIC_POSTFIX=.mic
[user@host] $ mpirun –f mpi_hosts –perhost 1 –n 2 test.exe
Hello world: rank 0 of 2 running on node0
Hello world: rank 1 of 2 running on node0-mic0

More details on these and other Xeon Phi coprocessor-specific environment variables are available in the Release Notes Addendum for MIC Architecture document available in the <intelmpi_install_dir>/doc directory, or online at our Release Notes page.