PetscViewerHDF5SetCollective#

Use collective MPI-IO transfer mode for HDF5 reads and writes.

Synopsis#

#include "petscviewerhdf5.h" 
PetscErrorCode PetscViewerHDF5SetCollective(PetscViewer viewer, PetscBool flg)

Logically Collective; flg must contain common value

Input Parameters#

viewer - the PetscViewer; if it is not PETSCVIEWERHDF5 then this command is ignored
flg - PETSC_TRUE for collective mode; PETSC_FALSE for independent mode (default)

Options Database Key#

-viewer_hdf5_collective - turns on (true) or off (false) collective transfers

Note#

Collective mode gives the MPI-IO layer underneath HDF5 a chance to do some additional collective optimizations and hence can perform better. However, this works correctly only since HDF5 1.10.3 and if HDF5 is installed for MPI; hence, we ignore this setting for older versions.

Developer Note#

In the HDF5 layer, PETSC_TRUE / PETSC_FALSE means H5Pset_dxpl_mpio() is called with H5FD_MPIO_COLLECTIVE / H5FD_MPIO_INDEPENDENT, respectively. This in turn means use of MPI_File_{read,write}all / MPI_File{read,write} in the MPI-IO layer, respectively. See HDF5 documentation and MPI-IO documentation for details.