[mpich-discuss] mpiexec and -n option

[Pavan Balaji]

On 08/16/2011 02:57 PM, Jain, Rohit wrote:
> I can! I am just trying to understand the need for it. Do I always
> need to use it?
>
> Documents are not clear about this usage. It looked like specifying
> host:<n> in host file might have worked here.

No, that's not the right usage. The "host:x" notation just says launch 
'x' processes on this host before you move to the next host. It has 
nothing to do with which executable is launched.

> So far, it looks like I always need to use '-n 1' option, when using
> 'exec : exec : exec' style launch, irrespective of binding methods,
> or host file specification. Is that correct?

By default, each executable gets the number of processes specified in 
the host file (or by the resource manager). This default makes sense for 
single-executable launches; for multi-executable launches I can't think 
of a good default value, so I decided not to change it.

So, yes, if you are not happy with the default value, you should use the 
"-n" option to specify how many processes you want.

  -- Pavan

-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji