hwlocality_memattrs(3) Hardware Locality (hwloc) hwlocality_memattrs(3)
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 = 0,
HWLOC_MEMATTR_ID_LOCALITY = 1, HWLOC_MEMATTR_ID_BANDWIDTH = 2,
HWLOC_MEMATTR_ID_LATENCY = 3 }
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.
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
No initiator is involved when looking at this attribute. The
corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST.
HWLOC_MEMATTR_ID_LOCALITY
No initiator is involved when looking at this attribute. The
corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST.
HWLOC_MEMATTR_ID_BANDWIDTH
HWLOC_MEMATTR_ID_LATENCY
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.
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 the attribute does not relate to a specific initiator (it does not
have the flag HWLOC_MEMATTR_FLAG_NEED_INITIATOR), -1 is returned and
errno is set to EINVAL.
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.
If there are no matching initiators, -1 is returned with errno set to
ENOENT;
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.
If there are no matching targets, -1 is returned with errno set to
ENOENT;
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.
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.
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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