33
NOTE:
The maximum number of instances supported on a single node is four.
NOTE:
When running multiple processes of a program on a single host, the processes
communicate using host memory, not the Ethernet. There is an upper limit on the size of
messages that can be sent between processes on the same host which depends on the number
of instances on the host and the total amount of physical memory.
On a system with 1G of
physical RAM, when running 2 instances on the same node, the upper limit is 32M bytes;
when running 3 instances on the same node, the upper limit is slightly more than 16M bytes;
when running 4 instances on the same node, the upper limit is slightly more than 8 M bytes.
See the Ammasso 1100 Technical Notes at
http://www.ammasso.com/support
for specific details about how this is determined, and how a user can modify these limits.
4.4.2 Remote Startup Service
AMSO_MPICH makes use of standard
rsh
(1) and
ssh
(1) remote execution services for
startup of remote MPI processes. This requires that each cluster node be accessible via
rsh(1)
or
ssh(1)
without the need to enter a password. You can verify that this is the
case by issuing a simple command,
e.g.
# rsh hostA hostname
hostA
The default remote execution service is selected during install. To change the remote
execution service dynamically, set the environment variable P4_RSHCOMMAND. For
example, using the bash shell:
# export P4_RSHCOMMAND=/usr/bin/ssh
4.5 Verifying MPI Installation
Once an application has been compiled and linked with the Ammasso MPICH driver, it can
be run like any other MPI application.
The example
cpi.c
program that was compiled and linked above on 2 systems can be used
to verify that the MPI installation is correct. The following commands may be used:
# cd <install_dir>/mpich-1.2.5/examples
# <install_dir>/mpich-1.2.5/bin/mpirun -np 2 ./cpi
Here
-np
specifies the number of processes with which to run the test. In this example two
(2) processes are specified. This number must be less than or equal to the number of lines in
the machines file created above.
The output from running the above program produces the following output: