On Apr 8, 2014, at 8:05 AM, Hamid Saeed <e.hamidsa...@gmail.com> wrote:
> Yes i meant Parallel file system. > > And can you kindly explain what exactly happens if > the RANK0 want to send to RANK0? It goes thru the "self" BTL, which is pretty fast but does require a little time You also have the collective operation overhead in the scatterv algorithm. > > Why does MPIO is different in time consumption than RANK0 to RANK0 > communication? Again, it depends on how you did the test. MPIO on a single node is just a file read operation - depending on the parallel file system, that can be heavily optimized with pre-fetch and memory caching. > > > On Tue, Apr 8, 2014 at 4:45 PM, Ralph Castain <r...@open-mpi.org> wrote: > 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 > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > > > > -- > _______________________________________________ > 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
