Ubuntu Manpage: hwloc - General information about hwloc ("hardware locality").

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
the same connotations as Linux's "CPU set" (e.g., process affinity, etc.).

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 3
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.

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.

Hex: 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.

I/O devices:
Locations may also be a PCI or OS object. The corresponding value is the set of CPUs that are
close to the physical device. For example, "pci=02:03.1" is equivalent to the set of
processors that are close to the hostbridge above PCI device with bus ID "02:03.1". "os=eth0"
is equivalent to all processors close to the network interface whose software name is "eth0".

Multiple locations can be specified on the command lines (delimited by whitespace); the first token of
the execution command is assumed to either follow "--" (if specified) or the first token that is
unrecognized as a location.

By default, if multiple locations are specified, they are added, meaning that the binding will be wider
in the sense that the process may run on more objects.

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.

"all" and "root" are special locations consisting in the root object in tree. It contains the entire
current topology. 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.

node A NUMA node; a set of processors around memory which the processors can directly access.

package Typically a physical package or chip, that goes into a package, it is a grouping of one or more
processors.

cache A cache memory. If several kinds of caches exist in the system, a specific one may be
identified by its level (e.g. l1cache) and optionally by its type (e.g. l1icache).

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).

The additional system type can be used when several machines form an overall single system image (SSI),
such as Kerrighed.

I/O devices are not listed here since they are not identified using tuples 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.

NAME

DESCRIPTION

SEE ALSO