SYNTAX

   C Syntax
          #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)

INPUT PARAMETERS

       • cvar_index: Index of the control variable to be queried.

INPUT/OUTPUT PARAMETERS

       • name_len: Length of the string and/or buffer for name.

       • desc_len: Length of the string and/or buffer for desc.

OUTPUT PARAMETERS

       • 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.

DESCRIPTION

       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.

VERBOSITY

       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):

       1. MPI_T_VERBOSITY_USER_BASIC: Basic information of interest to users

       2. MPI_T_VERBOSITY_USER_DETAIL: Detailed information of interest to users

       3. MPI_T_VERBOSITY_USER_ALL: All remaining information of interest to users

       4. MPI_T_VERBOSITY_TUNER_BASIC: Basic information required for tuning

       5. MPI_T_VERBOSITY_TUNER_DETAIL: Detailed information required for tuning

       6. MPI_T_VERBOSITY_TUNER_ALL: All remaining information required for tuning

       7. MPI_T_VERBOSITY_MPIDEV_BASIC: Basic information for MPI implementors

       8. MPI_T_VERBOSITY_MPIDEV_DETAIL: Detailed information for MPI implementors

       9. MPI_T_VERBOSITY_MPIDEV_ALL: All remaining information for MPI implementors

       For more information see MPI-3 section 14.3.1.

DATATYPE

       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 section 14.3.5.

SCOPE

       The  scope  describes  when and how changes can be made to a control variable. From MPI-3 section 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 section 14.3.6 Table 14.4.

NOTES

       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.

ERRORS

       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

       SEE ALSO:
          ompi_info

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                            MPI_T_CVAR_GET_INFO(3)