NAME

       hwlocality_memattrs - Comparing memory node attributes for finding where to allocate on

SYNOPSIS

   Data Structures
       struct hwloc_location

   Typedefs
       typedef unsigned hwloc_memattr_id_t

   Enumerations
       enum hwloc_memattr_id_e { HWLOC_MEMATTR_ID_CAPACITY, HWLOC_MEMATTR_ID_LOCALITY,
           HWLOC_MEMATTR_ID_BANDWIDTH, HWLOC_MEMATTR_ID_READ_BANDWIDTH,
           HWLOC_MEMATTR_ID_WRITE_BANDWIDTH, HWLOC_MEMATTR_ID_LATENCY,
           HWLOC_MEMATTR_ID_READ_LATENCY, HWLOC_MEMATTR_ID_WRITE_LATENCY, HWLOC_MEMATTR_ID_MAX }
       enum hwloc_location_type_e { HWLOC_LOCATION_TYPE_CPUSET, HWLOC_LOCATION_TYPE_OBJECT }
       enum hwloc_local_numanode_flag_e { HWLOC_LOCAL_NUMANODE_FLAG_LARGER_LOCALITY,
           HWLOC_LOCAL_NUMANODE_FLAG_SMALLER_LOCALITY, HWLOC_LOCAL_NUMANODE_FLAG_ALL }

   Functions
       int hwloc_memattr_get_by_name (hwloc_topology_t topology, const char *name,
           hwloc_memattr_id_t *id)
       int hwloc_get_local_numanode_objs (hwloc_topology_t topology, struct hwloc_location
           *location, unsigned *nr, hwloc_obj_t *nodes, unsigned long flags)
       int hwloc_memattr_get_value (hwloc_topology_t topology, hwloc_memattr_id_t attribute,
           hwloc_obj_t target_node, struct hwloc_location *initiator, unsigned long flags,
           hwloc_uint64_t *value)
       int hwloc_memattr_get_best_target (hwloc_topology_t topology, hwloc_memattr_id_t
           attribute, struct hwloc_location *initiator, unsigned long flags, hwloc_obj_t
           *best_target, hwloc_uint64_t *value)
       int hwloc_memattr_get_best_initiator (hwloc_topology_t topology, hwloc_memattr_id_t
           attribute, hwloc_obj_t target, unsigned long flags, struct hwloc_location
           *best_initiator, hwloc_uint64_t *value)

Detailed Description

       Platforms with heterogeneous memory require ways to decide whether a buffer should be
       allocated on 'fast' memory (such as HBM), 'normal' memory (DDR) or even 'slow' but large-
       capacity memory (non-volatile memory). These memory nodes are called 'Targets' while the
       CPU accessing them is called the 'Initiator'. Access performance depends on their locality
       (NUMA platforms) as well as the intrinsic performance of the targets (heterogeneous
       platforms).

       The following attributes describe the performance of memory accesses from an Initiator to
       a memory Target, for instance their latency or bandwidth. Initiators performing these
       memory accesses are usually some PUs or Cores (described as a CPU set). Hence a Core may
       choose where to allocate a memory buffer by comparing the attributes of different target
       memory nodes nearby.

       There are also some attributes that are system-wide. Their value does not depend on a
       specific initiator performing an access. The memory node Capacity is an example of such
       attribute without initiator.

       One way to use this API is to start with a cpuset describing the Cores where a program is
       bound. The best target NUMA node for allocating memory in this program on these Cores may
       be obtained by passing this cpuset as an initiator to hwloc_memattr_get_best_target() with
       the relevant memory attribute. For instance, if the code is latency limited, use the
       Latency attribute.

       A more flexible approach consists in getting the list of local NUMA nodes by passing this
       cpuset to hwloc_get_local_numanode_objs(). Attribute values for these nodes, if any, may
       then be obtained with hwloc_memattr_get_value() and manually compared with the desired
       criteria.

       Memory attributes are also used internally to build Memory Tiers which provide an easy way
       to distinguish NUMA nodes of different kinds, as explained in Heterogeneous Memory.

       See also
           An example is available in doc/examples/memory-attributes.c in the source tree.

       Note
           The API also supports specific objects as initiator, but it is currently not used
           internally by hwloc. Users may for instance use it to provide custom performance
           values for host memory accesses performed by GPUs.

           The interface actually also accepts targets that are not NUMA nodes.

Typedef Documentation

   typedef unsigned hwloc_memattr_id_t
       A memory attribute identifier. May be either one of hwloc_memattr_id_e or a new id
       returned by hwloc_memattr_register().

Enumeration Type Documentation

   enum hwloc_local_numanode_flag_e
       Flags for selecting target NUMA nodes.

       Enumerator

       HWLOC_LOCAL_NUMANODE_FLAG_LARGER_LOCALITY
              Select NUMA nodes whose locality is larger than the given cpuset. For instance, if
              a single PU (or its cpuset) is given in initiator, select all nodes close to the
              package that contains this PU.

       HWLOC_LOCAL_NUMANODE_FLAG_SMALLER_LOCALITY
              Select NUMA nodes whose locality is smaller than the given cpuset. For instance, if
              a package (or its cpuset) is given in initiator, also select nodes that are
              attached to only a half of that package.

       HWLOC_LOCAL_NUMANODE_FLAG_ALL
              Select all NUMA nodes in the topology. The initiator initiator is ignored.

   enum hwloc_location_type_e
       Type of location.

       Enumerator

       HWLOC_LOCATION_TYPE_CPUSET
              Location is given as a cpuset, in the location cpuset union field.

       HWLOC_LOCATION_TYPE_OBJECT
              Location is given as an object, in the location object union field.

   enum hwloc_memattr_id_e
       Memory node attributes.

       Enumerator

       HWLOC_MEMATTR_ID_CAPACITY
              The "Capacity" is returned in bytes (local_memory attribute in objects). Best
              capacity nodes are nodes with higher capacity.

       No initiator is involved when looking at this attribute. The corresponding attribute flags
       are HWLOC_MEMATTR_FLAG_HIGHER_FIRST.

       HWLOC_MEMATTR_ID_LOCALITY
              The "Locality" is returned as the number of PUs in that locality (e.g. the weight
              of its cpuset). Best locality nodes are nodes with smaller locality (nodes that are
              local to very few PUs). Poor locality nodes are nodes with larger locality (nodes
              that are local to the entire machine).

       No initiator is involved when looking at this attribute. The corresponding attribute flags
       are HWLOC_MEMATTR_FLAG_HIGHER_FIRST.

       HWLOC_MEMATTR_ID_BANDWIDTH
              The "Bandwidth" is returned in MiB/s, as seen from the given initiator location.
              Best bandwidth nodes are nodes with higher bandwidth.

       The corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST and
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR.

       This is the average bandwidth for read and write accesses. If the platform provides
       individual read and write bandwidths but no explicit average value, hwloc computes and
       returns the average.

       HWLOC_MEMATTR_ID_READ_BANDWIDTH
              The "ReadBandwidth" is returned in MiB/s, as seen from the given initiator
              location. Best bandwidth nodes are nodes with higher bandwidth.

       The corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST and
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR.

       HWLOC_MEMATTR_ID_WRITE_BANDWIDTH
              The "WriteBandwidth" is returned in MiB/s, as seen from the given initiator
              location. Best bandwidth nodes are nodes with higher bandwidth.

       The corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST and
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR.

       HWLOC_MEMATTR_ID_LATENCY
              The "Latency" is returned as nanoseconds, as seen from the given initiator
              location. Best latency nodes are nodes with smaller latency.

       The corresponding attribute flags are HWLOC_MEMATTR_FLAG_LOWER_FIRST and
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR.

       This is the average latency for read and write accesses. If the platform provides
       individual read and write latencies but no explicit average value, hwloc computes and
       returns the average.

       HWLOC_MEMATTR_ID_READ_LATENCY
              The "ReadLatency" is returned as nanoseconds, as seen from the given initiator
              location. Best latency nodes are nodes with smaller latency.

       The corresponding attribute flags are HWLOC_MEMATTR_FLAG_LOWER_FIRST and
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR.

       HWLOC_MEMATTR_ID_WRITE_LATENCY
              The "WriteLatency" is returned as nanoseconds, as seen from the given initiator
              location. Best latency nodes are nodes with smaller latency.

       The corresponding attribute flags are HWLOC_MEMATTR_FLAG_LOWER_FIRST and
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR.

Function Documentation

   int hwloc_get_local_numanode_objs (hwloc_topology_t topology, struct hwloc_location *
       location, unsigned * nr, hwloc_obj_t * nodes, unsigned long flags)
       Return an array of local NUMA nodes. By default only select the NUMA nodes whose locality
       is exactly the given location. More nodes may be selected if additional flags are given as
       a OR'ed set of hwloc_local_numanode_flag_e.

       If location is given as an explicit object, its CPU set is used to find NUMA nodes with
       the corresponding locality. If the object does not have a CPU set (e.g. I/O object), the
       CPU parent (where the I/O object is attached) is used.

       On input, nr points to the number of nodes that may be stored in the nodes array. On
       output, nr will be changed to the number of stored nodes, or the number of nodes that
       would have been stored if there were enough room.

       Returns
           0 on success or -1 on error.

       Note
           Some of these NUMA nodes may not have any memory attribute values and hence not be
           reported as actual targets in other functions.

           The number of NUMA nodes in the topology (obtained by hwloc_bitmap_weight() on the
           root object nodeset) may be used to allocate the nodes array.

           When an object CPU set is given as locality, for instance a Package, and when flags
           contain both HWLOC_LOCAL_NUMANODE_FLAG_LARGER_LOCALITY and
           HWLOC_LOCAL_NUMANODE_FLAG_SMALLER_LOCALITY, the returned array corresponds to the
           nodeset of that object.

   int hwloc_memattr_get_best_initiator (hwloc_topology_t topology, hwloc_memattr_id_t attribute,
       hwloc_obj_t target, unsigned long flags, struct hwloc_location * best_initiator,
       hwloc_uint64_t * value)
       Return the best initiator for the given attribute and target NUMA node. If value is non
       NULL, the corresponding value is returned there.

       If multiple initiators have the same attribute values, only one is returned (and there is
       no way to clarify how that one is chosen). Applications that want to detect initiators
       with identical/similar values, or that want to look at values for multiple attributes,
       should rather get all values using hwloc_memattr_get_value() and manually select the
       initiator they consider the best.

       The returned initiator should not be modified or freed, it belongs to the topology.

       flags must be 0 for now.

       Returns
           0 on success.

           -1 with errno set to ENOENT if there are no matching initiators.

           -1 with errno set to EINVAL if the attribute does not relate to a specific initiator
           (it does not have the flag HWLOC_MEMATTR_FLAG_NEED_INITIATOR).

   int hwloc_memattr_get_best_target (hwloc_topology_t topology, hwloc_memattr_id_t attribute,
       struct hwloc_location * initiator, unsigned long flags, hwloc_obj_t * best_target,
       hwloc_uint64_t * value)
       Return the best target NUMA node for the given attribute and initiator. If the attribute
       does not relate to a specific initiator (it does not have the flag
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR), location initiator is ignored and may be NULL.

       If value is non NULL, the corresponding value is returned there.

       If multiple targets have the same attribute values, only one is returned (and there is no
       way to clarify how that one is chosen). Applications that want to detect targets with
       identical/similar values, or that want to look at values for multiple attributes, should
       rather get all values using hwloc_memattr_get_value() and manually select the target they
       consider the best.

       flags must be 0 for now.

       Returns
           0 on success.

           -1 with errno set to ENOENT if there are no matching targets.

           -1 with errno set to EINVAL if flags are invalid, or no such attribute exists.

       Note
           The initiator initiator should be of type HWLOC_LOCATION_TYPE_CPUSET when refering to
           accesses performed by CPU cores. HWLOC_LOCATION_TYPE_OBJECT is currently unused
           internally by hwloc, but users may for instance use it to provide custom information
           about host memory accesses performed by GPUs.

   int hwloc_memattr_get_by_name (hwloc_topology_t topology, const char * name,
       hwloc_memattr_id_t * id)
       Return the identifier of the memory attribute with the given name.

       Returns
           0 on success.

           -1 with errno set to EINVAL if no such attribute exists.

   int hwloc_memattr_get_value (hwloc_topology_t topology, hwloc_memattr_id_t attribute,
       hwloc_obj_t target_node, struct hwloc_location * initiator, unsigned long flags,
       hwloc_uint64_t * value)
       Return an attribute value for a specific target NUMA node. If the attribute does not
       relate to a specific initiator (it does not have the flag
       HWLOC_MEMATTR_FLAG_NEED_INITIATOR), location initiator is ignored and may be NULL.

       flags must be 0 for now.

       Returns
           0 on success.

           -1 on error, for instance with errno set to EINVAL if flags are invalid or no such
           attribute exists.

       Note
           The initiator initiator should be of type HWLOC_LOCATION_TYPE_CPUSET when refering to
           accesses performed by CPU cores. HWLOC_LOCATION_TYPE_OBJECT is currently unused
           internally by hwloc, but users may for instance use it to provide custom information
           about host memory accesses performed by GPUs.

Author

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