# 18.2.361. MPI_T_pvar_get_info

MPI_T_pvar_get_info — Query information from a performance variable

## 18.2.361.1. SYNTAX

### 18.2.361.1.1. C Syntax

    #include <mpi.h>

    int MPI_T_pvar_get_info(int pvar_index, char *name, int *name_len,
                            int *verbosity, int *var_class, MPI_Datatype *datatype, MPI_T_enum *enumtype,
                            char *desc, int *desc_len, int *bind, int *readonly, int *continuous,
                            int *atomic)

## 18.2.361.2. INPUT PARAMETERS

- `pvar_index`: Index of the performance variable to be queried.

## 18.2.361.3. 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.

## 18.2.361.4. OUTPUT PARAMETERS

- `name`: Buffer to return the string containing the name of the performance variable.

- `verbosity`: Verbosity level of this variable.

- `var_class`: Class of performance variable.

- `datatype`: MPI datatype of the information stored in the performance variable.

- `enumtype`: Optional descriptor for enumeration information.

- `desc`: Buffer to return the string containing the description of the performance variable.

- `bind`: Type of MPI object to which this variable must be bound.

- `readonly`: Flag indicating whether the variable can be written/reset.

- `continuous`: Flag indicating whether the variable can be started and stopped or is continuously active.

- `atomic`: Flag indicating whether the variable can be atomically read and reset.

## 18.2.361.5. DESCRIPTION

MPI_T_pvar_get_info can be used to query information from a performance variable. The function returns the verbosity, class, datatype, enumeration type, and binding of the queried control variable in the arguments verbosity, var_class, datatype, enumtype, and bind respectively. Flags indicating whether the variable is read-only, continuous, or atomic are returns in readonly, continuous, and atomic accordingly. See MPI-3 section 14.3.7 for more information. See the man page for MPI_T_cvar_get_info for information on variable verbosity.

## 18.2.361.6. VARIABLE CLASS

Performance variables are categorized into classes which describe their initial value, valid types, and behavior. The class returned in the var_class parameter may be one of the following:

- `MPI_T_PVAR_CLASS_STATE`: Variable represents a set of discrete states that may be described by an enumerator. Variables of this class must be represented by an MPI_INT. The starting value is the current state of the variable.

- `MPI_T_PVAR_CLASS_LEVEL`: Variable represents the current utilization level of a resource. Variables of this class must be represented by an MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, or MPI_DOUBLE. The starting value is the current utilization level of the resource.

- `MPI_T_PVAR_CLASS_SIZE`: Variable represents the fixed size of a resource. Variables of this class are represented by an MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, or MPI_DOUBLE. The starting value is the current size of the resource.

- `MPI_T_PVAR_CLASS_PERCENTAGE`: Variable represents the current percentage utilization level of a resource. Variables of this class are represented by an MPI_DOUBLE. The starting value is the current percentage utilization of the resource.

- `MPI_T_PVAR_CLASS_HIGHWATERMARK`: Variable represents the high watermark of the utilization of a resource. Variables of this class are represented by an MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, or MPI_DOUBLE. The starting value is the current utilization of the resource.

- `MPI_T_PVAR_CLASS_HIGHWATERMARK`: Variable represents the low watermark of the utilization of a resource. Variables of this class are represented by an MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, or MPI_DOUBLE. The starting value is the current utilization of the resource.

- `MPI_T_PVAR_CLASS_COUNTER`: Variable represents a count of the number of occurrences of a specific event. Variables of this class are represented by an MPI_UNSIGNED, MPI_UNSIGNED_LONG, or MPI_UNSIGNED_LONG_LONG. The starting value is 0.

- `MPI_T_PVAR_CLASS_COUNTER`: Variable represents an aggregated value that represents a sum of arguments processed during a specific event. Variables of this class are represented by an MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, or MPI_DOUBLE. The starting value is 0.

- `MPI_T_PVAR_CLASS_TIMER`: Variable represents the aggregated time spent by the MPI implementation while processing an event, type of event, or section of code. Variables of this class are represented by an MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, or MPI_DOUBLE. If the variable is represented by an MPI_DOUBLE the units will be the same as those used by MPI_Wtime(). The starting value is 0.

- `MPI_T_PVAR_CLASS_GENERIC`: Variable does not fit into any other class. Can by represented by an type supported by the MPI tool information interface (see DATATYPE). Starting value is variable specific.

For more information see MPI-3 section 14.3.7.

## 18.2.361.7. DATATYPE

The datatype returned by MPI_T_pvar_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 the MPI Tool information interface see MPI-3 section 14.3.5.

## 18.2.361.8. BINDING

Performance variables may be bound to an MPI object. The binding returned in the bind parameter may be one of the following:

- `MPI_T_BIND_NO_OBJECT`: No object

- `MPI_T_BIND_MPI_COMM`: MPI communicator

- `MPI_T_BIND_MPI_DATATYPE`: MPI datatype

- `MPI_T_BIND_MPI_ERRHANDLER`: MPI error handler

- `MPI_T_BIND_MPI_FILE`: MPI file handle

- `MPI_T_BIND_MPI_GROUP`: MPI group

- `MPI_T_BIND_MPI_OP`: MPI reduction operator

- `MPI_T_BIND_MPI_REQUEST`: MPI request

- `MPI_T_BIND_MPI_WIN`: MPI window for one-sided communication

- `MPI_T_BIND_MPI_MESSAGE`: MPI message object

- `MPI_T_BIND_MPI_INFO`: MPI info object

For more information see MPI-3 section 14.3.2.

## 18.2.361.9. 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. For more information see MPI-3 section 14.3.3.

## 18.2.361.10. ERRORS

MPI_T_pvar_get_info will fail if:

- `MPI_T_ERR_NOT_INITIALIZED`: The MPI Tools interface not initialized

- `MPI_T_ERR_INVALID_INDEX`: The performance variable index is invalid

See also

- MPI_T_cvar_get_info