File Info

The opaque info object allows you to provide hints for optimization of your code, making it run faster or more efficiently, for example. These hints are set for each file, using the MPI_File_open, MPI_File_set_view, MPI_File_set_info, and MPI_File_delete routines. MPI_File_set_info sets new values for the specified file's hints. MPI_File_get_info returns all the hints that the system currently associates with the specified file.

When using UNIX files, Sun MPI I/O provides four hints for controlling how much buffer space it uses to satisfy I/O requests: noncoll_read_bufsize, noncoll_write_bufsize, coll_read_bufsize, and coll_write_bufsize. These hints may be tuned for your particular hardware configuration and application to improve performance for both noncollective and collective data accesses. For example, if your application uses a single MPI I/O call to request multiple noncontiguous chunks that form a regular strided pattern inthe file, you may want to adjust the noncoll_write_bufsize to match the size of the stride. Note that these hints limit the size of MPI I/O's underlying buffers but do not limit the size of how much data a user can read or write in asingle request.