+1 on what Gilles said. A little more detail:
1. You can simply write your own "MPI_Bcast" and interpose your version before
Open MPI's version. E.g.,:
-----
$ cat your_program.c
#include <mpi.h>
int MPI_Bcast(void *buffer, int count, MPI_Datatype datatype,
int root, MPI_Comm comm)
{
// Whatever you want your Bcast to do
}
int main(int argc, char* argv[])
{
MPI_Init(NULL, NULL);
MPI_Bcast(...);
MPI_Finalize()
return 0;
}
-----
If you need to call MPI functions inside your MPI_Bcast, call them with "PMPI"
instead of "MPI". E.g., call "PMPI_Send(...)" instead of "MPI_Send(...)".
This guarantees that the back-end Open MPI versions of those functions will be
called instead of your versions (if you end up overriding more than MPI_Bcast,
for example).
I showed a trivial example above where everything is in one file -- but you can
also do more complicated examples where you group all your MPI_* function
overrides in a library that you link before/to the left of the actual Open MPI
library on the command line.
2. As Gilles mentioned, you can write your own Open MPI collectives component.
This will have the back-end Open MPI infrastructure call your routine(s) when
MPI_Bcast (and friends) are invoked by the application.
Option #2 is a bit more complex than option #1. If you're just looking to test
some algorithms and generally play around a little, option #1 is probably what
you want to do.
> On Feb 4, 2016, at 5:42 AM, Gilles Gouaillardet
> <[email protected]> wrote:
>
> Hi,
>
> this is difficult to answer such a generic request.
>
> MPI symbols (MPI_Bcast, ...) are defined as weak symbols, so the simplest
> option is to redefine them an implement them the way you like. you are always
> able to invoke PMPI_Bcast if you want to invoke the openmpi implementation.
>
> a more ompi-ish way is to create your own collective module.
> for example, the default module is in ompi/mca/coll/tuned
>
> Cheers,
>
> Gilles
>
> On Thursday, February 4, 2016, <[email protected]> wrote:
> Hello
>
> Using a new network interface and its ad-hoc routing algorithms I would like
> to try my own custom implementation of some collective communication
> patterns(MPI_Bcast,MPI_Alltoall,...) without expanding those collective
> communications as series of point-to-point ones based on a given predefined
> process topology.
>
> In addition my routing methods might require additional parameters, rather
> than the basic destination lists obtained from that topology and the kind of
> collective communication considered.
>
> How would I do that ?
>
> In which component should I modilfy something ?
>
>
> Regards
>
>
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--
Jeff Squyres
[email protected]
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