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

Provided by: libhwloc-doc_2.10.0-1build1_all

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.

Author

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Hardware Locality (hwloc)                        Version 2.10.0                           hwlocality_memattrs(3)