hints.c

The example for Boor USING MPI2

#include "mpi.h"
int main( int argc, char *argv[] )
{
    MPI_File fh;  
    MPI_Info info;

    MPI_Init( &argc, &argv );
    
    /* ... */
    MPI_Info_create(&info);

    /* FOLLOWING HINTS ARE PREDEFINED IN MPI */
    
    /* no. of I/O devices across which the file should be striped */
    MPI_Info_set(info, "striping_factor", "4");
    
    /* the striping unit in bytes */
    MPI_Info_set(info, "striping_unit", "65536");

    /* buffer size for collective I/O */
    MPI_Info_set(info, "cb_buffer_size", "8388608");

    /* no. of processes that should perform disk accesses 
       during collective I/O */
    MPI_Info_set(info, "cb_nodes", "4");

    /* FOLLOWING ARE ADDITIONAL HINTS SUPPORTED BY ROMIO */

    /* the I/O-device from which to start striping the file */
    MPI_Info_set(info, "start_iodevice", "2");

    /* buffer size for data sieving in independent reads */
    MPI_Info_set(info, "ind_rd_buffer_size", "2097152");
    
    /* buffer size for data sieving in independent writes */
    MPI_Info_set(info, "ind_wr_buffer_size", "1048576");

    /* use direct I/O on SGI's XFS file system 
       (platform-specific hints) */
    MPI_Info_set(info, "direct_read", "true");
    MPI_Info_set(info, "direct_write", "true");

    /* NOW OPEN THE FILE WITH THIS INFO OBJECT */
    MPI_File_open(MPI_COMM_WORLD, "/pfs/datafile", 
		  MPI_MODE_CREATE | MPI_MODE_RDWR, info, &fh);
    
    MPI_Info_free(&info);  /* free the info object */

    /* ... access file ... */

    MPI_File_close( &fh );

    /* ... */
    MPI_Finalize();
    return 0;
}