[mpich-discuss] MPI on a cluster of dual-CPU machines

[Christina Patrick]

Hi,

Just one more question though. You say that the latest release detects
this configuration. I am using mpich2-1.0.8. Does this version too
detect the presence of dual CPUs automatically?
I have made quite a few code changes to this version and don't really
want to migrate at this point. Hence I really need to know this.

Thanks and Regards,
Christina.

On Fri, Jul 17, 2009 at 6:56 PM, Pavan Balaji<balaji at mcs.anl.gov> wrote:
>
>> What is the most efficient way of doing this ... which options should
>> I specify while configuring the software and how do I specify the
>> options to mpdboot and mpiexec to use this feature of MPI ?
>
> Just use the default configuration in the latest release of MPICH2; it'll
> automatically figure out that there are multiple CPUs on the same node. For
> mpdboot, there are different ways of specifying this:
>
> $ cat hostfile
> host1
> host2
>
> ... this means that the first process will be on host1, second on host2,
> then the third process will go back to host1, the fourth on host2, etc.
>
> Another way is:
>
> $ cat hostfile
> host1:2
> host2:2
>
> ... this means that the first two processes will be on host1, and the next
> two on host2.
>
> If you are using the second way, make sure you use the --ncpus option to
> mpdboot.
>
>  $ mpdboot -f hostfile -n 2 --ncpus=2
>
>  $ mpiexec -n 4 ./app
>
> Also remember that the "-n" option in mpdboot specifies the number of
> physical nodes, and not the number of CPUs, while in mpiexec, it refers to
> the number of processes.
>
> If you don't want to deal with all these things, an alternate approach is to
> bypass mpd and use the new Hydra process manager. You can just do:
>
> $ mpiexec.hydra -f hostfile -n 4 ./app
>
> ... you won't need mpdboot in this case.
>
> Hope that helps.
>
>  -- Pavan
>
> --
> Pavan Balaji
> http://www.mcs.anl.gov/~balaji
>