Intel® MPI Library Developer Guide for Linux* OS

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ID 768728
Date 10/31/2024
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Document Table of Contents
Document Table of Contents x
Intel® MPI Library Developer Guide for Linux* OS
Intel® MPI Library Developer Guide for Linux* OS x
Introduction Installation and Prerequisites Compiling and Linking Running Applications Debugging Applications Analysis and Tuning Troubleshooting Additional Supported Features Examples Notices and Disclaimers
Introduction x
Introducing Intel® MPI Library Conventions and Symbols Related Information
Installation and Prerequisites x
Installation Prerequisite Steps
Compiling and Linking x
Compiling an MPI Program Compilers Support ILP64 Support
Running Applications x
Running Intel® MPI Library in Containers Selecting a Library Configuration Running an MPI Program Running an MPI/OpenMP* Program MPMD Launch Mode Fabrics Control Job Schedulers Support Controlling Process Placement Specifying Hosts Using a Machine File Using Argument Sets See Also Java* MPI Applications Support
Running Intel® MPI Library in Containers x
Build a Singularity* Container for an MPI Application Run the Application with a Container
Fabrics Control x
Selecting Fabrics Libfabric* Support OFI* Providers Support
Debugging Applications x
Debugging Using -gtool for Debugging
Analysis and Tuning x
Displaying MPI Debug Information Tracing Applications Interoperability with Other Tools Through -gtool MPI Tuning
Troubleshooting x
Error Message: Bad Termination Error Message: No such file or Directory Error Message: Permission Denied Error Message: Fatal Error Error Message: Bad File Descriptor Error Message: Too Many Open Files Problem: High Memory Consumption Readings Problem: MPI Application Hangs Problem: Password Required Problem: Cannot Execute Binary File Problem: MPI limitation for Docker*
Additional Supported Features x
Asynchronous Progress Control Device-Initiated Communications Notified One-Sided Communications Multiple Endpoints Support
Multiple Endpoints Support x
MPI_THREAD_SPLIT Programming Model Threading Runtimes Support Program Examples Code Change Guide
Examples x
async_progress_sample.c thread_split.cpp thread_split_omp_for.c thread_split_omp_task.c thread_split_pthreads.c
Intel® MPI Library Developer Guide for Linux* OS

Controlling Process Placement

Placement of MPI processes over the cluster nodes plays a significant role in application performance. Intel® MPI Library provides several options to control process placement.

By default, when you run an MPI program, the process manager launches all MPI processes specified with -n on the current node. If you use a job scheduler, processes are assigned according to the information received from the scheduler.

Specifying Hosts

You can explicitly specify the nodes on which you want to run the application using the -hosts option. This option takes a comma-separated list of node names as an argument. Use the -ppn option to specify the number of processes per node. For example: 

$ mpirun  -n 4 -ppn 2 -hosts node1,node2 ./testc 
Hello world: rank 0 of 4 running on node1
Hello world: rank 1 of 4 running on node1
Hello world: rank 2 of 4 running on node2
Hello world: rank 3 of 4 running on node2

To get the name of a node, use the hostname utility.

An alternative to using the -hosts option is creation of a host file that lists the cluster nodes. The format of the file is one name per line, and the lines starting with # are ignored. Use the -f option to pass the file to mpirun. For example: 

$ cat ./hosts
#nodes
node1
node2
$ mpirun  -n 4 -ppn 2 -f hosts ./testc

This program launch produces the same output as the previous example.

If the -ppn option is not specified, the process manager assigns as many processes to the first node as there are physical cores on it. Then the next node is used. That is, assuming there are four cores on node1 and you launch six processes overall, four processes are launched on node1, and the remaining two processes are launched on node2. For example: 

$ mpirun -n 6 -hosts node1,node2 ./testc
Hello world: rank 0 of 6 running on node1
Hello world: rank 1 of 6 running on node1
Hello world: rank 2 of 6 running on node1
Hello world: rank 3 of 6 running on node1
Hello world: rank 4 of 6 running on node2
Hello world: rank 5 of 6 running on node2
NOTE:
If you use a job scheduler, specifying hosts is unnecessary. The processes manager uses the host list provided by the scheduler.

Using a Machine File

A machine file is similar to a host file with the only difference that you can assign a specific number of processes to particular nodes directly in the file. Contents of a sample machine file may look as follows: 

$ cat ./machines
node1:2
node2:2

Specify the file with the -machine option. Running a simple test program produces the following output: 

$ mpirun  -machine machines ./testc
Hello world: rank 0 of 4 running on node1
Hello world: rank 1 of 4 running on node1
Hello world: rank 2 of 4 running on node2
Hello world: rank 3 of 4 running on node2

Using Argument Sets

Argument sets are unique groups of arguments specific to a particular node. Combined together, the argument sets make up a single MPI job. You can provide argument sets on the command line, or in a configuration file. To specify a node, use the -host option.

On the command line, argument sets should be separated by a colon ':'. Global options (applied to all argument sets) should appear first, and local options (applied only to the current argument set) should be specified within an argument set. For example: 

$ mpirun  -genv I_MPI_DEBUG=2 -host node1 -n 2 ./testc  : -host node2 -n 2 ./testc

In the configuration file, each argument set should appear on a new line. Global options should appear on the first line of the file. For example: 

$ cat ./config 
-genv I_MPI_DEBUG=2-host node1 -n 2 ./testc
-host node2 -n 2 ./testc

Specify the configuration file with the -configfile option: 

$ mpirun -configfile config
Hello world: rank 0 of 4 running on node1
Hello world: rank 1 of 4 running on node1
Hello world: rank 2 of 4 running on node2
Hello world: rank 3 of 4 running on node2
Parent topic: Running Applications
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