Manpages - MPI_T_cvar_get_info.3

MPI_T_cvar_get_info - Query information from a control variable

  #include <mpi.h>
  int MPI_T_cvar_get_info(int cvar_index, char *name, int *name_len,
                          int *verbosity, MPI_Datatype *datatype, MPI_T_enum *enumtype,
                          const *desc, int *desc_len, int *bind, int *scope)

cvar_index

Index of the control variable to be queried.

name_len

Length of the string and/or buffer for name.

desc_len

Length of the string and/or buffer for desc.

name

Buffer to return the string containing the name of the control variable.

verbosity

Verbosity level of this variable.

datatype

MPI datatype of the information stored in the control variable.

enumtype

Optional descriptor for enumeration information.

desc

Buffer to return the string containing the description of the control variable.

bind

Type of MPI object to which this variable must be bound.

scope

Scope of when changes to this variable are possible.

MPI_T_cvar_get_info can be used to query information about a control variable. The function returns the verbosity, datatype, enumeration type, binding, and scope of the queried control variable in the arguments verbosity, datatype, enumtype, bind, and scope, respectively. Control variables in Open MPI are the same as MCA parameters.

As Open MPI exposes a very large number of MCA parameters (control variables), control variables are categorized into nine verbosity levels corresponding to the equivalent ompi_info level. The nine levels are (in increasing order):

MPI_T_VERBOSITY_USER_BASIC

Basic information of interest to users

MPI_T_VERBOSITY_USER_DETAIL

Detailed information of interest to users

MPI_T_VERBOSITY_USER_ALL

All remaining information of interest to users

MPI_T_VERBOSITY_TUNER_BASIC

Basic information required for tuning

MPI_T_VERBOSITY_TUNER_DETAIL

Detailed information required for tuning

MPI_T_VERBOSITY_TUNER_ALL

All remaining information required for tuning

MPI_T_VERBOSITY_MPIDEV_BASIC

Basic information for MPI implementors

MPI_T_VERBOSITY_MPIDEV_DETAIL

Detailed information for MPI implementors

MPI_T_VERBOSITY_MPIDEV_ALL

All remaining information for MPI implementors

For more information see MPI-3 � 14.3.1.

The datatype returned by MPI_T_cvar_get_info is restricted to one of the following datatypes: MPI_INT, MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, MPI_COUNT, MPI_CHAR, and MPI_DOUBLE. For more information on datatypes in MPI_T see MPI-3 � 14.3.5.

The scope describes when and how changes can be made to a control variable. From MPI-3 � 14.3.6, the scope may be any of the following:

MPI_T_SCOPE_CONSTANT

read-only, value is constant

MPI_T_SCOPE_READONLY

read-only, cannot be written, but can change

MPI_T_SCOPE_LOCAL

may be writeable, writing is a local operation

MPI_T_SCOPE_GROUP

may be writeable, must be done to a group of processes, all processes in a group must be set to consistent values

MPI_T_SCOPE_GROUP_EQ

may be writeable, must be done to a group of processes, all processes in a group must be set to the same value

MPI_T_SCOPE_ALL

may be writeable, must be done to all processes, all connected processes must be set to consistent values

MPI_T_SCOPE_ALL_EQ

may be writeable, must be done to all processes, all connected processes must be set to the same value

For more information see MPI-3 � 14.3.6 Table 14.4.

This MPI tool interface function returns two strings. This function takes two argument for each string: a buffer to store the string, and a length which must initially specify the size of the buffer. If the length passed is n then this function will copy at most n - 1 characters of the string into the corresponding buffer and set the length to the number of characters copied - 1. If the length argument is NULL or the value specified in the length is 0 the corresponding string buffer is ignored and the string is not returned.

Open MPI does not currently support binding control variables to MPI objects.

MPI_T_cvar_get_info() will fail if:

[MPI_T_ERR_NOT_INITIALIZED]

The MPI Tools interface not initialized

[MPI_T_ERR_INVALID_INDEX]

The control variable index is invalid

  ompi_info