- Created by Barbara Jones, last modified on Aug 09, 2019
H5P_GET_MPIO_NO_COLLECTIVE_CAUSE
Retrieves local and global causes that broke collective I/O on the last parallel I/O call
Procedure:
H5P_GET_MPIO_NO_COLLECTIVE_CAUSE( dxpl_id, local_no_collective_cause, global_no_collective_cause )
Signature:
herr_t H5Pget_mpio_no_collective_cause(
hid_t dxpl_id,
uint32_t * local_no_collective_cause,
uint32_t * global_no_collective_cause)
Parameters:
hid_t dxpl_id | IN: Dataset transfer property list identifier |
uint32_t *local_no_collective_cause | OUT: An enumerated set value indicating the causes that prevented collective I/O in the local process |
uint32_t *global_no_collective_cause | OUT: An enumerated set value indicating the causes across all processes that prevented collective I/O |
Motivation:
A user can request collective I/O via a data transfer property list (DXPL) that has been suitably modified with H5P_SET_DXPL_MPIO. However, there are conditions that can cause HDF5 to forgo collective I/O and perform independent I/O. Such causes can be different across the processes of a parallel application. This function allows the user to determine what caused the HDF5 library to skip collective I/O locally, that is in the local process, and globally, across all processes.
Description:
H5P_GET_MPIO_NO_COLLECTIVE_CAUSE serves two purposes. It can be used to determine whether collective I/O was used for the last preceding parallel I/O call. If collective I/O was not used, the function retrieves the local and global causes that broke collective I/O on that parallel I/O call. The properties retrieved by this function are set before I/O takes place and are retained even when I/O fails.
Valid values returned in local_no_collective_cause and global_no_collective_cause are as follows or, if there are multiple causes, a bitwise OR of the relevant causes; the numbers in the center column are the bitmask values:
H5D_MPIO_COLLECTIVE | 00000000 | Collective I/O was performed successfully (Default) |
H5D_MPIO_SET_INDEPENDENT | 00000001 | Collective I/O was not performed because independent I/O was requested |
H5D_MPIO_DATATYPE_CONVERSION | 00000010 | Collective I/O was not performed because datatype conversions were required |
H5D_MPIO_DATA_TRANSFORMS | 00000100 | Collective I/O was not performed because data transforms needed to be applied |
H5D_MPIO_SET_MPIPOSIX | 00001000 | Collective I/O was not performed because the selected file driver was MPI-POSIX |
H5D_MPIO_NOT_SIMPLE_OR_SCALAR_DATASPACES | 00010000 | Collective I/O was not performed because one of the dataspaces was neither simple nor scalar |
H5D_MPIO_POINT_SELECTIONS | 00100000 | Collective I/O was not performed because there were point selections in one of the dataspaces |
H5D_MPIO_NOT_CONTIGUOUS_OR_CHUNKED_DATASET | 01000000 | Collective I/O was not performed because the dataset was neither contiguous nor chunked |
H5D_MPIO_FILTERS | 10000000 | Collective I/O was not performed because filters needed to be applied |
The above name/value pairs are members of HDF5’s H5D_mpio_no_collective_cause_t enumeration.
Each process determines whether it can perform collective I/O and broadcasts the result. Those results are combined to make a collective decision; collective I/O will be performed only if all processes can perform collective I/O.
If collective I/O was not used, the causes that prevented it are reported by individual process by means of an enumerated set. The causes may differ among processes, so H5P_GET_MPIO_NO_COLLECTIVE_CAUSE returns two property values. The first value is the one produced by the local process to report local causes. This local information is encoded in an enumeration, the H5D_mpio_no_collective_cause_t described above, with all individual causes combined into a single enumeration value by means of a bitwise OR operation. The second value reports global causes; this global value is the result of a bitwise-OR operation across the values returned by all the processes.
Returns:
Returns a non-negative value if successful; otherwise returns a negative value.
Example:
/* Get the cause of broken collective I/O */
ret = H5Pget_mpio_no_collective_cause (dxpl_write, &no_collective_cause_local_write, &no_collective_cause_global_write);
History:
| Release | Change |
|---|---|
| 1.8.10 | C function introduced in this release. |
--- Last Modified: August 09, 2019 | 12:48 PM