[mpich-discuss] Re : MPI I/O vs Sequential I/O

[Rajeev Thakur]

megabytes, gigabytes.

On Mar 20, 2013, at 6:13 PM, Muhammad Zulfikar Handana wrote:

> 
> exactly how big the files are great for use on a comparison of MPI I / O?
> 
> thank a lot for your attention
> 
> handana
> 
> fwrite() does buffered I/O, which will perform better for small writes. A better comparison would be to use write(), which is what MPI-IO uses internally.
> 
> Rajeev
> 
> On Mar 18, 2013, at 3:49 PM, Muhammad Zulfikar Handana wrote:
> 
> > hello, i have some questions about MPI-I/O.
> >
> > 1) when i trying execute my program using MPI-I/O. why when iam execute
> > with 1 proses, execute time more good than when iam execute with 2 proses.
> > am i wrong? this is my source code.
> >        MPI_File_open (MPI_COMM_WORLD, file_akhir, MPI_MODE_CREATE |
> > MPI_MODE_WRONLY, MPI_INFO_NULL, &hasil);
> >         int jumlah1 = (((block-1)*16)+pad);
> >            int  jumlah = jumlah1 / size;
> >
> >
> >               MPI_File_set_view(hasil, rank * jumlah *
> > sizeof(char),MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL);
> >               MPI_File_write (hasil, output, jumlah1, MPI_CHAR,
> > MPI_STATUS_IGNORE);
> >
> >         MPI_File_close(&hasil);
> >
> > 2) and after that i have compared that source using MPI - I/O and with
> > sequential I/O, apparently, sequential i / o is better than the parallel i
> > / o. how it could be happen? this is my sequential source.
> > if (rank==0) {
> >
> >         hasil = fopen (file_akhir, "wb");
> >         int test = (((block-1)*16)+pad);
> >           fwrite (output, sizeof(char), test, hasil );
> >        fclose (hasil);
> >      }
> >
> > thanks a lot for your attention
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