Noncontiguous I/O Accesses Through MPI-IO

I/O performance remains a weakness of parallel computing systems today. While this weakness is partly attributed to rapid advances in other system components, I/O interfaces available to programmers and the I/O methods supported by file systems have traditionally not matched efficiently with the types of I/O operations that scientific applications perform, particularly noncontiguous accesses. The MPI-IO interface allows for rich descriptions of the I/O patterns desired for scientific applications and implementations such as ROMIO have taken advantage of this ability while remaining limited by underlying file system methods. A method of noncontiguous data access, list I/O, was recently implemented in the Parallel Virtual File System (PVFS). We implement support for this interface in the ROMIO MPI-IO implementation. Through a suite of noncontiguous I/O tests we compared ROMIO list I/O to current methods of ROMIO noncontiguous access and found that the list I/O interface provides performance benefits in many noncontiguous cases.