As I said, the degree of impact depends on the messaging pattern. If rank A typically sends/recvs with rank A+!, then you won't see much difference. However, if rank A typically sends/recvs with rank N-A, where N=#ranks in job, then you'll see a very large difference.
You might try simply changing the mapping pattern - e.g., add -bynode to your cmd line. This would make it run faster if it followed the latter example. On Nov 2, 2013, at 12:40 AM, San B <forum....@gmail.com> wrote: > Yes MM... But here a single node has 16cores not 64 cores. > The 1st two jobs were with OMPI-1.4.5. > 16 cores of single node - 3692.403 > 16 cores on two nodes (8 cores per node) - 12338.809 > > The 1st two jobs were with OMPI-1.6.5. > 16 cores of single node - 3547.879 > 16 cores on two nodes (8 cores per node) - 5527.320 > > As others said, due to shared memory communication the single node job > is running faster, but I was expecting a slight difference between 1 & 2 > nodes - which is taking 60% more time here. > > > > On Thu, Oct 31, 2013 at 8:19 PM, Ralph Castain <r...@open-mpi.org> wrote: > Yes, though the degree of impact obviously depends on the messaging pattern > of the app. > > On Oct 31, 2013, at 2:50 AM, MM <finjulh...@gmail.com> wrote: > >> Of course, by this you mean, with the same total number of nodes, for e.g. >> 64 process on 1 node using shared mem, vs 64 processes spread over 2 nodes >> (32 each for e.g.)? >> >> >> On 29 October 2013 14:37, Ralph Castain <r...@open-mpi.org> wrote: >> As someone previously noted, apps will always run slower on multiple nodes >> vs everything on a single node due to the shared memory vs IB differences. >> Nothing you can do about that one. >> _______________________________________________ >> >> users mailing list >> us...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/users > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
