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3 – Using InfiniPath MPI
InfiniPath MPI Details
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programs will be started on that host before using the next entry in the mpihosts
file. If the full
mpihosts file is processed, and there are still more processes
requested, processing starts again at the start of the file.
You have several alternative ways of specifying the
mpihosts file.
1. First, as noted in section 3.3.1, you can use the command line option
-m:
$
mpirun -np n -m mpihosts [other options] program-name
In this case, if the named file cannot be opened, the MPI job fails.
2. If the
-m option is omitted, mpirun checks the environment variable MPIHOSTS
for the name of the MPI hosts file. If this variable is defined and the file it names
cannot be opened, then the MPI job fails.
3. In the absence of both the
-m option and the MPIHOSTS environment variable,
mpirun uses the file ./mpihosts, if it exists.
4. If none of these three methods of specifying the hosts file are used,
mpirun
looks for the file
~/.mpihosts.
If you are working in the context of a batch queuing system, it may provide you with
a job submission script that generates an appropriate
mpihosts file.
3.5.7
Console I/O in MPI Programs
mpirun sends any output printed to stdout or stderr by any node program to the
terminal. This output is line-buffered, so the lines output from the various node
programs will be non-deterministically interleaved on the terminal. Using the
-l
option to mpirun will label each line with the rank of the node program that produced
it.
Node programs do not normally use interactive input on
stdin, and by default,
stdin is bound to /dev/null. However, for applications that require standard input
redirection, InfiniPath MPI supports two mechanisms to redirect stdin:
1. If
mpirun is run from the same node as MPI rank 0, all input piped to the mpirun
command will be redirected to rank 0.
2. If
mpirun is not run from the same node as MPI rank 0 or if the input must be
redirected to all or specific MPI processes, the
-stdin option can be used to
redirect a file as standard input to all nodes or to a particular node as specified
by the
-stdin-target option.
3.5.8
Environment for Node Programs
The environment variables existing on the front end node on which you run mpirun
are not propagated to the other nodes. You can set the paths, such as