getting rid of hard-coded MPI_COMM_WORLD

Axel akoh... at
Wed Dec 5 16:59:08 CET 2007

On Dec 5, 4:17 am, Fawzi Mohamed <fa... at> wrote:

hi fawzi,

> I wrote the f77_interface trying to exactly achieve that.

right. i should have mentioned, that i realized 99% of what
i have in mind is already done (great job, BTW. it is always
too easy to forget acknowledging that one is only worrying
about a tiny detail).

> There are two routines to create force_envs one that recieves
> explicitly a group (actually a communicator, in cp2k we have it
> sistematically misnomed) and another that has no arguments (and
> defaults to MPI_COMM_WORLD).
> This is actually already used internally in cp2k and should work.
> If it doesn't then it should definitly be fixed.

yep. i'll look into it and will probably only find out, once
i have a prototype code to try it out. my question was mainly
intended to find out, whether there was a technical reason to
do everything as it is done now.

> Or you want to change the init routine (wich just defines a general
> fallback in case of really bad errors)?

yep. i'd also like to enter the init routine with a group
i am thinking about working on a code that would control multiple
MPI-parallelized codes, so the "supervisor" code would need to hog
the world communicator, partition it into suitable groups and hand
a group communicator to each code.

that being said, the fact that cp2k _is_ already 99% independent of
any hardcoded communicators is - apart from the features - the reason
why we are considering it in the first place. ;-)

thanks and cheers,

> Fawzi
> On Dec 5, 2007, at 12:57 AM, Axel wrote:
> > hi!
> > this is a RFC to the cp2k developers that hang out here.
> > i'd like to change the code, so that cp2k can be run from
> > a "supervisor" MPI program. that would mean to get rid of
> > the (few!) hardcoded MPI_COMM_WORLD constants in
> > message_passing.F and f77_interface.F so that one can
> > launch a cp2k calculation on a group communicator (which
> > of course would default to MPI_COMM_WORLD).
> > any comments, suggestions, caveats would be highly appreciated.
> > thanks,
> >    axel.

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