Dear Xing Feng, there are different algorithms to implement collective communication patterns. Next to general Big-O complexity the concrete complexity also depends on the network topology, message length, etc..
Therefore many MPI implementations switch between different algorithms depending on the concrete communication parameters in a call. A colleague of mine investigated some MPI implementations (though not OpenMPI) [1]. There you can see how different MPI implementations (IBM, ParaStation, Cray) scale differently for a selection of collective calls. Maybe that helps a little in understanding the performance of your application. Cheers, Marc-Andre [1] http://dl.acm.org/citation.cfm?doid=2751205.2751216 On 30.09.15 07:53, XingFENG wrote: > Hi, every one, > > I am working with open-mpi. When I tried to analyse performance of my > programs, I find it is hard to understand the communication complexity > of MPI routines. > > I have found some page on Internet such as > http://stackoverflow.com/questions/10625643/mpi-communication-complexity > > > This indicates that communication complexity of broadcasting an > integer is O(log P) where P is the number of processes. But is it > correct on different MPI implementations( OMPI, MPICH, etc.)? Is there > an official document discussing such complexity? > > > -- > Best Regards. > --- > Xing FENG > PhD Candidate > Database Research Group > > School of Computer Science and Engineering > University of New South Wales > NSW 2052, Sydney > > Phone: (+61) 413 857 288 > > > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: > http://www.open-mpi.org/community/lists/users/2015/09/27719.php > -- Marc-Andre Hermanns Jülich Aachen Research Alliance, High Performance Computing (JARA-HPC) German Research School for Simulation Sciences GmbH Schinkelstrasse 2 52062 Aachen Germany Phone: +49 2461 61 2509 Fax: +49 241 80 6 99753 www.grs-sim.de/parallel email: m.a.herma...@grs-sim.de
smime.p7s
Description: S/MIME Cryptographic Signature
