NAME

       hwlocality_distances_get - 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',
       'XGMIHops' 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

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