This option implicitly sets the max_slots value (maximum number of available slots) to the same value as the slots value for each node, as specified in your hostfile. Oversubscribing a host is not suggested, as it might result in performance degradation. If you schedule more processes to run than there are available slots, this is referred to as oversubscribing. Note - If you use these two options ( -hostfile and -host) together, make sure that the host(s) you specify using the -host option also exist in the hostfile. This command launches one instance of a.out on host c, but excludes the other hosts in the hostfile (a, b, and d). % mpirun -np 1 -hostfile my_hosts -host c a.out For example, the following command directs mpirun to run a program called a.out on hosts a, b, and c: You can use the -host option to mpirun to specify the hosts you want to use on the command line in a comma-delimited list. Specifying Hosts By Using the -host Option See the comments in the hostfile for more information. It is empty by default, but you may edit this file to add your list of nodes. Unless you specify a different hostfile at a different location, this is the hostfile that OpenMPI uses. Note - Open MPI includes a commented default hostfile at /opt/SUNWhpc/HPC8.0/etc/openmpi-default-hostfile. Resource managers also do not specify the maximum number of available slots.
Open MPI assumes that the maximum number of slots you can specify is equal to infinity, unless explicitly specified. It overrides the values for max_slots set in the hostfile. When you use this hostfile with the -nooversubscribe option (see Oversubscribing Nodes), mpirun assumes that the value of max_slots for each node in the hostfile is the same as the value of slots for each node. The four slots on node3 can be oversubscribed, up to a maximum of 20 processes. This disallows the processors on node2 from being oversubscribed. node2 and node3 both have 4 slots, but the values of slots and max_slots are the same (4) on node2. In this example file, node0 is a single-processor machine. For example, the following listing shows a simple hostfile: The hostfile lists each node, the available number of slots, and the maximum number of slots on that node. Use this option to specify which hosts to include or exclude. The hostfile is a text file that contains the names of hosts, the number of available slots on each host, and the maximum slots on each host.
To determine where the processes will run, ORTE uses the following criteria: When you issue the mpirun command from the command line, ORTE reads the number of processes to be launched from the -np option, and then determines where the processes will run. To run the program with default settings, enter the command and program name, followed by any required arguments to the program: To specify the list of hosts on which to execute the program (also known as the rankmap file) To specify the list of hosts on which to invoke processes (also known as the rankmap string) TABLE 5-1 Program/Process Control Options The procedures that follow the table explain how these options are used and show the syntax for each. The following table shows the process control options for the mpirun command.
HOW TO INSTALL MPI ON WINDOWS HOW TO
The examples in this section show how to use the mpirun command options to specify how and where the processes and programs run.
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