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NAME
hwloc - General information about hwloc ("hardware locality").
DESCRIPTION
hwloc provides command line tools and a C API to obtain the hierarchical map of key
computing elements, such as: NUMA memory nodes, shared caches, processor packages,
processor cores, and processor "threads". hwloc also gathers various attributes such as
cache and memory information, and is portable across a variety of different operating
systems and platforms.
Definitions
hwloc has some specific definitions for terms that are used in this man page and other
hwloc documentation.
hwloc CPU set:
A set of processors included in an hwloc object, expressed as a bitmask indexed by
the physical numbers of the CPUs (as announced by the OS). The hwloc definition of
"CPU set" does not carry any of the same connotations as Linux's "CPU set" (e.g.,
process affinity, cgroup, etc.).
hwloc node set:
A set of NUMA memory nodes near an hwloc object, expressed as a bitmask indexed by
the physical numbers of the NUMA nodes (as announced by the OS).
Linux CPU set:
See http://www.mjmwired.net/kernel/Documentation/cpusets.txt for a discussion of
Linux CPU sets. A super-short-ignoring-many-details description (taken from that
page) is:
"Cpusets provide a mechanism for assigning a set of CPUs and Memory Nodes to a set
of tasks."
Linux Cgroup:
See http://www.mjmwired.net/kernel/Documentation/cgroups.txt for a discussion of
Linux control groups. A super-short-ignoring-many-details description (taken from
that page) is:
"Control Groups provide a mechanism for aggregating/partitioning sets of tasks, and
all their future children, into hierarchical groups with specialized behaviour."
To be clear, hwloc supports all of the above concepts. It is simply worth noting that
they are different things.
Location Specification
Locations refer to specific regions within a topology. Before reading the rest of this
man page, it may be useful to read lstopo(1) and/or run lstopo on your machine to see the
reported topology tree. Seeing and understanding a topology tree will definitely help in
understanding the concepts that are discussed below.
Locations can be specified in multiple ways:
Tuples: Tuples of hwloc "objects" and associated indexes can be specified in the form
object:index. hwloc objects represent types of mapped items (e.g., packages,
cores, etc.) in a topology tree; indexes are non-negative integers that specify
a unique physical object in a topology tree. Both concepts are described in
detail, below.
Some filters may be added after the type to further specify which objects are
wanted. <type>[subtype=<subtype>] selects objects matching the given type and
also its subtype string attribute. For instance NUMA[HBM] selects NUMA nodes of
subtype "HBM". The prefix subtype= may be avoided if there is no ambiguity.
NUMA[tier=X] selects NUMA nodes of tier <X> ("MemoryTier" info attribute).
Indexes may also be specified as ranges. x-y enumerates from index x to y. x:y
enumerates y objects starting from index x (wrapping around the end of the index
range if needed). x- enumerates all objects starting from index x. all, odd,
and even are also supported for listing all objects, or only those with odd or
even indexes.
Chaining multiple tuples together in the more general form
object1:index[.object2:index2[...]] is permissable. While the first tuple's
object may appear anywhere in the topology, the Nth tuple's object must have a
shallower topology depth than the (N+1)th tuple's object. Put simply: as you
move right in a tuple chain, objects must go deeper in the topology tree. When
using logical indexes (which is the default), indexes specified in chained
tuples are relative to the scope of the parent object. For example,
"package:0.core:1" refers to the second core in the first package.
When using OS/physical indexes, the first object matching the given index is
used.
PCI and OS devices may also be designed using their identifier. For example,
"pci=02:03.1" is the PCI device with bus ID "02:03.1". "os=eth0" is the network
interface whose software name is "eth0". PCI devices may also be filtered based
on their vendor and/or device IDs, for instance "pci[15b3:]:2" for the third
Mellanox PCI device (vendor ID 0x15b3). OS devices may also be filtered based
on their subtype, for instance "os[gpu]:all" for all GPU OS devices.
Hex: For tools that manipulate object as sets (e.g. hwloc-calc and hwloc-bind),
locations can also be specified as hexidecimal bitmasks prefixed with "0x".
Commas must be used to separate the hex digits into blocks of 8, such as
"0xffc0140,0x00020110". Leading zeros in each block do not need to be
specified. For example, "0xffc0140,0x20110" is equivalent to the prior example,
and "0x0000000f" is exactly equivalent to "0xf". Intermediate blocks of 8
digits that are all zeoro can be left empty; "0xff0,,0x13" is equivalent to
"0xff0,0x00000000,0x13". If the location is prefixed with the special string
"0xf...f", then all unspecified bits are set (as if the set were infinite). For
example, "0xf...f,0x1" sets both the first bit and all bits starting with the
33rd. The string "0xf...f" -- with no other specified values -- sets all bits.
"all" and "root" are special locations consisting in the root object in tree. It contains
the entire current topology.
Some tools directly operate on these objects (e.g. hwloc-info and hwloc-annotate). They
do not support hexadecimal locations because each location may correspond to multiple
objects. For instance, there can be exactly one L3 cache per package and NUMA node, which
means it's the same location. If multiple locations are given on the command-line, these
tools will operation on each location individually and consecutively.
Some other tools internally manipulate objects as sets (e.g. hwloc-calc and hwloc-bind).
They translate each input location into a hexidecimal location. When I/O or Misc objects
are used, they are translated into the set of processors (or NUMA nodes) that are close to
the given object (because I/O or Misc objects do not contain processors or NUMA nodes).
If multiple locations are specified on the command-line (delimited by whitespace), they
are combined (the overall location is wider). If prefixed with "~", the given location
will be cleared instead of added to the current list of locations. If prefixed with "x",
the given location will be and'ed instead of added to the current list. If prefixed with
"^", the given location will be xor'ed.
More complex operations may be performed by using hwloc-calc to compute intermediate
values.
hwloc Objects
Objects in tuples can be any of the following strings (listed from "biggest" to
"smallest"):
machine A set of processors and memory.
numanode A NUMA node; a set of processors around memory which the processors can directly
access. If numa[hbm] is used instead of numanode in locations, command-line
tools only consider NUMA nodes marked as high-bandwidth memory (subtype "HBM").
package Typically a physical package or chip, that goes into a package, it is a grouping
of one or more processors.
l1cache ... l5cache
A data (or unified) cache.
l1icache ... l3icache
An instruction cache.
core A single, physical processing unit which may still contain multiple logical
processors, such as hardware threads.
pu Short for processor unit (not process!). The smallest physical execution unit
that hwloc recognizes. For example, there may be multiple PUs on a core (e.g.,
hardware threads).
osdev, pcidev, bridge, and misc may also be used to specify special devices although some
of them have dedicated identification ways as explained in Location Specification.
Finally, note that an object can be denoted by its numeric "depth" in the topology graph.
hwloc Indexes
Indexes are integer values that uniquely specify a given object of a specific type.
Indexes can be expressed either as logical values or physical values. Most hwloc
utilities accept logical indexes by default. Passing --physical switches to physical/OS
indexes. Both logical and physical indexes are described on this man page.
Logical indexes are relative to the object order in the output from the lstopo command.
They always start with 0 and increment by 1 for each successive object.
Physical indexes are how the operating system refers to objects. Note that while physical
indexes are non-negative integer values, the hardware and/or operating system may choose
arbitrary values -- they may not start with 0, and successive objects may not have
consecutive values.
For example, if the first few lines of lstopo -p output are the following:
Machine (47GB)
NUMANode P#0 (24GB) + Package P#0 + L3 (12MB)
L2 (256KB) + L1 (32KB) + Core P#0 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#1 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#2 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#8 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#9 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#10 + PU P#0
NUMANode P#1 (24GB) + Package P#1 + L3 (12MB)
L2 (256KB) + L1 (32KB) + Core P#0 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#1 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#2 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#8 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#9 + PU P#0
L2 (256KB) + L1 (32KB) + Core P#10 + PU P#0
In this example, the first core on the second package is logically number 6 (i.e.,
logically the 7th core, starting from 0). Its physical index is 0, but note that another
core also has a physical index of 0. Hence, physical indexes may only be relevant within
the scope of their parent (or set of ancestors). In this example, to uniquely identify
logical core 6 with physical indexes, you must specify (at a minimum) both a package and a
core: package 1, core 0.
Index values, regardless of whether they are logical or physical, can be expressed in
several different forms (where X, Y, and N are positive integers):
X The object with index value X.
X-Y All the objects with index values >= X and <= Y.
X- All the objects with index values >= X.
X:N N objects starting with index X, possibly wrapping around the end of the level.
all A special index value indicating all valid index values.
odd A special index value indicating all valid odd index values.
even A special index value indicating all valid even index values.
REMEMBER: hwloc's command line tools accept logical indexes for location values by
default. Use --physical and --logical to switch from one mode to another.
SEE ALSO
hwloc's command line tool documentation: lstopo(1), hwloc-bind(1), hwloc-calc(1), hwloc-
distrib(1), hwloc-ps(1).
hwloc has many C API functions, each of which have their own man page. Some top-level man
pages are also provided, grouping similar functions together. A few good places to start
might include: hwlocality_objects(3), hwlocality_types(3), hwlocality_creation(3),
hwlocality_cpuset(3), hwlocality_information(3), and hwlocality_binding(3).
For a listing of all available hwloc man pages, look at all "hwloc*" files in the man1 and
man3 directories.