I suspect it all depends on when you start the clock. If the data is sitting in the file at time=0, then the file I/O method will likely be faster as every proc just reads its data in parallel - no comm required as it is all handled by the parallel file system.
I confess I don't quite understand your reference to "shared memory" in the MPIO case, but I suspect what you really meant was just "parallel file system"? On Apr 8, 2014, at 6:12 AM, Hamid Saeed <e.hamidsa...@gmail.com> wrote: > Can someone kindly reply? > > > > On Tue, Apr 8, 2014 at 1:01 PM, Hamid Saeed <e.hamidsa...@gmail.com> wrote: > Hello, > I think that the MPI open its sockets even though the number of processor is > only 1 on the same machine? > regards. > > > On Tue, Apr 8, 2014 at 9:43 AM, Hamid Saeed <e.hamidsa...@gmail.com> wrote: > Hello all, > > I have a very basic question regarding MPI communication. > > In my Task, what i am doing is.. > Comparing Scatterv and MPIO. > 1) In scatterv, I scatter all the data to the other ranks and SCAN for the > specific characters. > MPI_Scatterv (chunk, send_counts, displacements, MPI_CHAR, copychunk, > smallchunk_size, MPI_CHAR, 0, MPI_COMM_WORLD); > & > 2) On the other hand using MPIO, I have the data available in the shared > memory and every rank searches in the specific chunk. > MPI_File_open(MPI_COMM_WORLD, "170mb.txt", MPI_MODE_RDONLY, MPI_INFO_NULL, > &in); > here i assign every processor to search in a specific "chunk" > > > My question is.. > > Why MPI_Scatterv using 1 processor takes more time then MPI_File_open? > How does MPI sending and receiving takes place? > > I think using 1 processor does not include physical sending and receiving. > Then why it consumes more clock? > > In the attachment you can observe the plots in which i performed some tests > using both algorithms. > > Kindly explain briefly the mpi communication using 1 processor and multiple > processors. > > > Thanks in advance. > > Regards > Hamid > > > > -- > Hamid > > > > > -- > _______________________________________________ > Hamid Saeed > CoSynth GmbH & Co. KG > Escherweg 2 - 26121 Oldenburg - Germany > Tel +49 441 9722 738 | Fax -278 > http://www.cosynth.com > _______________________________________________ > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
