# hwloc_get_latency (3) - Linux Manuals

## hwloc_get_latency: Manipulating Distances

## NAME

hwlocality_distances - Manipulating Distances

### Functions

static const struct **hwloc_distances_s** * **hwloc_get_whole_distance_matrix_by_depth** (**hwloc_topology_t** topology, unsigned depth)

static const struct **hwloc_distances_s** * **hwloc_get_whole_distance_matrix_by_type** (**hwloc_topology_t** topology, **hwloc_obj_type_t** type)

static const struct **hwloc_distances_s** * **hwloc_get_distance_matrix_covering_obj_by_depth** (**hwloc_topology_t** topology, **hwloc_obj_t** obj, unsigned depth, unsigned *firstp)

static int **hwloc_get_latency** (**hwloc_topology_t** topology, **hwloc_obj_t** obj1, **hwloc_obj_t** obj2, float *latency, float *reverse_latency)

## Detailed Description

## Function Documentation

### static const struct **hwloc_distances_s*** hwloc_get_distance_matrix_covering_obj_by_depth (**hwloc_topology_t** topology, **hwloc_obj_t** obj, unsigned depth, unsigned * firstp) [static]

Get distances for the given depth and covering some objects. Return a distance matrix that describes depth depth and covers at least object obj and all its children.

When looking for the distance between some objects, a common ancestor should be passed in obj.

firstp is set to logical index of the first object described by the matrix.

The returned structure belongs to the hwloc library. The caller should not modify or free it.

### static int hwloc_get_latency (**hwloc_topology_t** topology, **hwloc_obj_t** obj1, **hwloc_obj_t** obj2, float * latency, float * reverse_latency) [inline], [static]

Get the latency in both directions between two objects. Look at ancestor objects from the bottom to the top until one of them contains a distance matrix that matches the objects exactly.

latency gets the value from object obj1 to obj2, while reverse_latency gets the reverse-direction value, which may be different on some architectures.

**Returns:**

- -1 if no ancestor contains a matching latency matrix.

### static const struct **hwloc_distances_s*** hwloc_get_whole_distance_matrix_by_depth (**hwloc_topology_t** topology, unsigned depth) [static]

Get the distances between all objects at the given depth.

**Returns:**

- a distances structure containing a matrix with all distances between all objects at the given depth.

Slot i+nbobjs*j contains the distance from the object of logical index i the object of logical index j.

**Note:**

- This function only returns matrices covering the whole topology, without any unknown distance value. Those matrices are available in top-level object of the hierarchy. Matrices of lower objects are not reported here since they cover only part of the machine.

The returned structure belongs to the hwloc library. The caller should not modify or free it.

**Returns:**

- NULL if no such distance matrix exists.

### static const struct **hwloc_distances_s*** hwloc_get_whole_distance_matrix_by_type (**hwloc_topology_t** topology, **hwloc_obj_type_t** type) [static]

Get the distances between all objects of a given type.

**Returns:**

- a distances structure containing a matrix with all distances between all objects of the given type.

Slot i+nbobjs*j contains the distance from the object of logical index i the object of logical index j.

**Note:**

- This function only returns matrices covering the whole topology, without any unknown distance value. Those matrices are available in top-level object of the hierarchy. Matrices of lower objects are not reported here since they cover only part of the machine.

The returned structure belongs to the hwloc library. The caller should not modify or free it.

**Returns:**

- NULL if no such distance matrix exists.

## Author

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