# hwlocality_distances_get - Man Page

Retrieve distances between objects

## Synopsis

### Data Structures

struct **hwloc_distances_s**

### Enumerations

enum **hwloc_distances_kind_e** { **HWLOC_DISTANCES_KIND_FROM_OS**, **HWLOC_DISTANCES_KIND_FROM_USER**, **HWLOC_DISTANCES_KIND_MEANS_LATENCY**, **HWLOC_DISTANCES_KIND_MEANS_BANDWIDTH**, **HWLOC_DISTANCES_KIND_HETEROGENEOUS_TYPES** }

enum **hwloc_distances_transform_e** { **HWLOC_DISTANCES_TRANSFORM_REMOVE_NULL**, **HWLOC_DISTANCES_TRANSFORM_LINKS**, **HWLOC_DISTANCES_TRANSFORM_MERGE_SWITCH_PORTS**, **HWLOC_DISTANCES_TRANSFORM_TRANSITIVE_CLOSURE** }

### Functions

int **hwloc_distances_get** (**hwloc_topology_t** topology, unsigned *nr, struct **hwloc_distances_s** **distances, unsigned long kind, unsigned long flags)

int **hwloc_distances_get_by_depth** (**hwloc_topology_t** topology, int depth, unsigned *nr, struct **hwloc_distances_s** **distances, unsigned long kind, unsigned long flags)

int **hwloc_distances_get_by_type** (**hwloc_topology_t** topology, **hwloc_obj_type_t** type, unsigned *nr, struct **hwloc_distances_s** **distances, unsigned long kind, unsigned long flags)

int **hwloc_distances_get_by_name** (**hwloc_topology_t** topology, const char *name, unsigned *nr, struct **hwloc_distances_s** **distances, unsigned long flags)

const char * **hwloc_distances_get_name** (**hwloc_topology_t** topology, struct **hwloc_distances_s** *distances)

void **hwloc_distances_release** (**hwloc_topology_t** topology, struct **hwloc_distances_s** *distances)

int **hwloc_distances_transform** (**hwloc_topology_t** topology, struct **hwloc_distances_s** *distances, enum **hwloc_distances_transform_e** transform, void *transform_attr, unsigned long flags)

## Detailed Description

## Enumeration Type Documentation

### enum hwloc_distances_kind_e

Kinds of distance matrices. The `kind`

attribute of struct **hwloc_distances_s** is a OR'ed set of kinds.

A kind of format HWLOC_DISTANCES_KIND_FROM_* specifies where the distance information comes from, if known.

A kind of format HWLOC_DISTANCES_KIND_MEANS_* specifies whether values are latencies or bandwidths, if applicable.

**Enumerator**

*HWLOC_DISTANCES_KIND_FROM_OS*These distances were obtained from the operating system or hardware.

*HWLOC_DISTANCES_KIND_FROM_USER*These distances were provided by the user.

*HWLOC_DISTANCES_KIND_MEANS_LATENCY*Distance values are similar to latencies between objects. Values are smaller for closer objects, hence minimal on the diagonal of the matrix (distance between an object and itself). It could also be the number of network hops between objects, etc.

*HWLOC_DISTANCES_KIND_MEANS_BANDWIDTH*Distance values are similar to bandwidths between objects. Values are higher for closer objects, hence maximal on the diagonal of the matrix (distance between an object and itself). Such values are currently ignored for distance-based grouping.

*HWLOC_DISTANCES_KIND_HETEROGENEOUS_TYPES*This distances structure covers objects of different types. This may apply to the 'NVLinkBandwidth' structure in presence of a NVSwitch or POWER processor NVLink port.

### enum hwloc_distances_transform_e

Transformations of distances structures.

**Enumerator**

*HWLOC_DISTANCES_TRANSFORM_REMOVE_NULL*Remove

`NULL`

objects from the distances structure. Every object that was replaced with`NULL`

in the`objs`

array is removed and the`values`

array is updated accordingly.

At least `2`

objects must remain, otherwise **hwloc_distances_transform()** will return `-1`

with `errno`

set to `EINVAL`

.

`kind`

will be updated with or without **HWLOC_DISTANCES_KIND_HETEROGENEOUS_TYPES** according to the remaining objects.

*HWLOC_DISTANCES_TRANSFORM_LINKS*Replace bandwidth values with a number of links. Usually all values will be either

`0`

(no link) or`1`

(one link). However some matrices could get larger values if some pairs of peers are connected by different numbers of links.

Values on the diagonal are set to `0`

.

This transformation only applies to bandwidth matrices.

*HWLOC_DISTANCES_TRANSFORM_MERGE_SWITCH_PORTS*Merge switches with multiple ports into a single object. This currently only applies to NVSwitches where GPUs seem connected to different separate switch ports in the NVLinkBandwidth matrix. This transformation will replace all of them with the same port connected to all GPUs. Other ports are removed by applying

**HWLOC_DISTANCES_TRANSFORM_REMOVE_NULL**internally.*HWLOC_DISTANCES_TRANSFORM_TRANSITIVE_CLOSURE*Apply a transitive closure to the matrix to connect objects across switches. This currently only applies to GPUs and NVSwitches in the NVLinkBandwidth matrix. All pairs of GPUs will be reported as directly connected.

## Function Documentation

### int hwloc_distances_get (hwloc_topology_t topology, unsigned * nr, struct hwloc_distances_s ** distances, unsigned long kind, unsigned long flags)

Retrieve distance matrices. Retrieve distance matrices from the topology into the `distances`

array.

`flags`

is currently unused, should be `0`

.

`kind`

serves as a filter. If `0`

, all distance matrices are returned. If it contains some HWLOC_DISTANCES_KIND_FROM_*, only distance matrices whose kind matches one of these are returned. If it contains some HWLOC_DISTANCES_KIND_MEANS_*, only distance matrices whose kind matches one of these are returned.

On input, `nr`

points to the number of distance matrices that may be stored in `distances`

. On output, `nr`

points to the number of distance matrices that were actually found, even if some of them couldn't be stored in `distances`

. Distance matrices that couldn't be stored are ignored, but the function still returns success (`0`

). The caller may find out by comparing the value pointed by `nr`

before and after the function call.

Each distance matrix returned in the `distances`

array should be released by the caller using **hwloc_distances_release()**.

### int hwloc_distances_get_by_depth (hwloc_topology_t topology, int depth, unsigned * nr, struct hwloc_distances_s ** distances, unsigned long kind, unsigned long flags)

Retrieve distance matrices for object at a specific depth in the topology. Identical to **hwloc_distances_get()** with the additional `depth`

filter.

### int hwloc_distances_get_by_name (hwloc_topology_t topology, const char * name, unsigned * nr, struct hwloc_distances_s ** distances, unsigned long flags)

Retrieve a distance matrix with the given name. Usually only one distances structure may match a given name.

The name of the most common structure is 'NUMALatency'. Others include 'XGMIBandwidth' and 'NVLinkBandwidth'.

### int hwloc_distances_get_by_type (hwloc_topology_t topology, hwloc_obj_type_t type, unsigned * nr, struct hwloc_distances_s ** distances, unsigned long kind, unsigned long flags)

Retrieve distance matrices for object of a specific type. Identical to **hwloc_distances_get()** with the additional `type`

filter.

### const char* hwloc_distances_get_name (hwloc_topology_t topology, struct hwloc_distances_s * distances)

Get a description of what a distances structure contains. For instance 'NUMALatency' for hardware-provided NUMA distances (ACPI SLIT), or NULL if unknown.

### void hwloc_distances_release (hwloc_topology_t topology, struct hwloc_distances_s * distances)

Release a distance matrix structure previously returned by **hwloc_distances_get()**.

**Note**This function is not required if the structure is removed with

**hwloc_distances_release_remove()**.

### int hwloc_distances_transform (hwloc_topology_t topology, struct hwloc_distances_s * distances, enum hwloc_distances_transform_e transform, void * transform_attr, unsigned long flags)

Apply a transformation to a distances structure. Modify a distances structure that was previously obtained with **hwloc_distances_get()** or one of its variants.

This modifies the local copy of the distances structures but does not modify the distances information stored inside the topology (retrieved by another call to **hwloc_distances_get()** or exported to XML). To do so, one should add a new distances structure with same name, kind, objects and values (see **Add distances between objects**) and then remove this old one with **hwloc_distances_release_remove()**.

`transform`

must be one of the transformations listed in **hwloc_distances_transform_e**.

These transformations may modify the contents of the `objs`

or `values`

arrays.

`transform_attr`

must be `NULL`

for now.

`flags`

must be `0`

for now.

**Note**Objects in distances array

`objs`

may be directly modified in place without using**hwloc_distances_transform()**. One may use**hwloc_get_obj_with_same_locality()**to easily convert between similar objects of different types.

## Author

Generated automatically by Doxygen for Hardware Locality (hwloc) from the source code.

## Referenced By

The man pages hwloc_distances_get(3), hwloc_distances_get_by_depth(3), hwloc_distances_get_by_name(3), hwloc_distances_get_by_type(3), hwloc_distances_get_name(3), hwloc_distances_kind_e(3), HWLOC_DISTANCES_KIND_FROM_OS(3), HWLOC_DISTANCES_KIND_FROM_USER(3), HWLOC_DISTANCES_KIND_MEANS_BANDWIDTH(3), HWLOC_DISTANCES_KIND_MEANS_LATENCY(3), hwloc_distances_release(3), hwloc_distances_transform(3), hwloc_distances_transform_e(3), HWLOC_DISTANCES_TRANSFORM_LINKS(3), HWLOC_DISTANCES_TRANSFORM_MERGE_SWITCH_PORTS(3), HWLOC_DISTANCES_TRANSFORM_REMOVE_NULL(3) and HWLOC_DISTANCES_TRANSFORM_TRANSITIVE_CLOSURE(3) are aliases of hwlocality_distances_get(3).