Unless your cluster has some weird connection topology and you're trying to take advantage of that, collective is the best bet.
On Mon, Dec 13, 2010 at 4:26 PM, Eugene Loh <eugene....@oracle.com> wrote: > David Mathog wrote: > > Is there a rule of thumb for when it is best to contact N workers with >> MPI_Bcast vs. when it is best to use a loop which cycles N times and >> moves the same information with MPI_Send to one worker at a time? >> >> > The rule of thumb is to use a collective whenever you can. The rationale > is that the programming should be easier/cleaner and the underlying MPI > implementation has the opportunity to do something clever. > > > For that matter, other than the coding semantics, is there any real >> difference between the two approaches? That is, does MPI_Bcast really >> broadcast, daisy chain, or use other similar methods to reduce bandwidth >> use when distributing its message, or does it just go ahead and run >> MPI_Send in a loop anyway, but hide the details from the programmer? >> >> I believe most MPI implementations, including OMPI, make an attempt to > "do the right thing". Multiple algorithms are available and the best one is > chosen based on run-time conditions. > > With any luck, you're better off with collective calls. Of course, there > are no guarantees. > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > -- David Zhang University of California, San Diego
