[mpich-discuss] Hydra: prefer localhost instead of first in host file

[Pavan Balaji]

Hi Torquil,

mpiexec -n 4 prog.exe (without any host file option) will always run 
processes on the local node.

I'm assuming you are setting the host file asking Hydra to use hostA, 
followed by hostB, followed by hostC. Hydra is doing exactly that. If 
you don't want Hydra to do that, you should remove the hostfile option.

  -- Pavan

On 03/27/2011 09:07 AM, Torquil Macdonald Sørensen wrote:
> Hi!
>
> I'm in an environment with multiple computers sharing the same filesystem.
>
> I'm using the latest Mpich2 with hydra and a host file that looks like
>
> hostA:4
> hostB:4
> hostC:4
>
> The host file is the same on all the computers, because it is on a shared
> filesystem.
>
> Sometimes I want to run with 12 processes and in that case this works fine.
>
> However, sometime I want only 4 processes, and I would like them to run on the
> computer I'm currently logged into (not always hostA). E.g. I want "mpiexec -n 4
> prog.exe" to start 4 processes on hostB if I run this command from hostB.
>
> That way, I can e.g. run three different simulations, each of 4 processes, each
> on its own computer, just by executing "mpiexec -n 4 prog.exe" on each
> individual computer.
>
> With earlier versions of Mpich2 this seemed to work as I wished (not using Hydra).
>
> Is there a way of making Mpich2 prefer to start the first 4 process on the local
> machine instead of starting them on the computer listed first in the host file?
>
> I'v been reading the Hydra documentation, obviously without finding out if this
> can be accomplished.
>
> Best regards
> Torquil Sørensen
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-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji