[Users] parallel program

[Jan Hegewald]

Hello,

Am 05.12.2006 um 11:43 schrieb Erik Schnetter:

> There are MPI versions that you can use across very different  
> machines, such as MPICH (I think) or MPICH-G2, built on Globus.   
> That is, instead of making different MPI versions interact, you  
> would build the interoperability into MPI itself.

well, but most clusters come with a vendor specific mpi  
implementation (e.g. the SGI systems) which one wants to use for  
maximum perfomance. Sure, I could install MPICH on every cluster to  
get a homogeneous  MPI environment, but that is only a bad worlaround  
IMHO.

> The reason for this is probably that our simulations are mostly  
> tightly coupled simulations, and we currently don't change the  
> number of participating processors once a run has started.   
> However, this is not a restriction of Cactus itself, it is mostly a  
> restriction of the drivers we use.

Actually MPI2 can do this e.g. via the spawn command, but be warned:  
communication to spawned machines is slower compared tho that of  
machines which where included on startup.

Cheers,
-- Jan