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https://github.com/open-mpi/hwloc

Hardware locality (hwloc)
https://github.com/open-mpi/hwloc

c hardware hpc locality topology

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Hardware locality (hwloc)

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README 

        
This is a truncated and poorly-formatted version of the documentation main page.

See https://www.open-mpi.org/projects/hwloc/doc/ for more.



hwloc Overview



The Hardware Locality (hwloc) software project aims at easing the process of

discovering hardware resources in parallel architectures. It offers

command-line tools and a C API for consulting these resources, their locality,

attributes, and interconnection. hwloc primarily aims at helping

high-performance computing (HPC) applications, but is also applicable to any

project seeking to exploit code and/or data locality on modern computing

platforms.



hwloc provides command line tools and a C API to obtain the hierarchical map of

key computing elements within a node, such as: NUMA memory nodes, shared

caches, processor packages, dies and cores, processing units (logical

processors or "threads") and even I/O devices. hwloc also gathers various

attributes such as cache and memory information, and is portable across a

variety of different operating systems and platforms.



hwloc primarily aims at helping high-performance computing (HPC) applications,

but is also applicable to any project seeking to exploit code and/or data

locality on modern computing platforms.



hwloc supports the following operating systems:



  * Linux (with knowledge of cgroups and cpusets, memory targets/initiators,

 etc.) on all supported hardware, including Intel Xeon Phi, ScaleMP vSMP,

 and NumaScale NumaConnect.

  * Solaris (with support for processor sets and logical domains)

  * AIX

  * Darwin / OS X

  * FreeBSD and its variants (such as kFreeBSD/GNU)

  * NetBSD

  * HP-UX

  * Microsoft Windows



Since it uses standard Operating System information, hwloc's support is mostly

independant from the processor type (x86, powerpc, ...) and just relies on the

Operating System support. The main exception is BSD operating systems (NetBSD,

FreeBSD, etc.) because they do not provide support topology information, hence

hwloc uses an x86-only CPUID-based backend (which can be used for other OSes

too, see the Components and plugins section).



To check whether hwloc works on a particular machine, just try to build it and

run lstopo or lstopo-no-graphics. If some things do not look right (e.g. bogus

or missing cache information), see Questions and Bugs.



hwloc only reports the number of processors on unsupported operating systems;

no topology information is available.



For development and debugging purposes, hwloc also offers the ability to work

on "fake" topologies:



  * Symmetrical tree of resources generated from a list of level arities, see

 Synthetic topologies.

  * Remote machine simulation through the gathering of topology as XML files,

 see Importing and exporting topologies from/to XML files.



hwloc can display the topology in a human-readable format, either in graphical

mode (X11), or by exporting in one of several different formats, including:

plain text, LaTeX tikzpicture, PDF, PNG, and FIG (see Command-line Examples

below). Note that some of the export formats require additional support

libraries.



hwloc offers a programming interface for manipulating topologies and objects.

It also brings a powerful CPU bitmap API that is used to describe topology

objects location on physical/logical processors. See the Programming Interface

below. It may also be used to binding applications onto certain cores or memory

nodes. Several utility programs are also provided to ease command-line

manipulation of topology objects, binding of processes, and so on.



Bindings for several other languages are available from the project website.



Command-line Examples



On a 4-package 2-core machine with hyper-threading, the lstopo tool may show

the following graphical output:



[dudley]



Here's the equivalent output in textual form:



Machine

  NUMANode L#0 (P#0)

  Package L#0 + L3 L#0 (4096KB)

 L2 L#0 (1024KB) + L1 L#0 (16KB) + Core L#0

   PU L#0 (P#0)

   PU L#1 (P#8)

 L2 L#1 (1024KB) + L1 L#1 (16KB) + Core L#1

   PU L#2 (P#4)

   PU L#3 (P#12)

  Package L#1 + L3 L#1 (4096KB)

 L2 L#2 (1024KB) + L1 L#2 (16KB) + Core L#2

   PU L#4 (P#1)

   PU L#5 (P#9)

 L2 L#3 (1024KB) + L1 L#3 (16KB) + Core L#3

   PU L#6 (P#5)

   PU L#7 (P#13)

  Package L#2 + L3 L#2 (4096KB)

 L2 L#4 (1024KB) + L1 L#4 (16KB) + Core L#4

   PU L#8 (P#2)

   PU L#9 (P#10)

 L2 L#5 (1024KB) + L1 L#5 (16KB) + Core L#5

   PU L#10 (P#6)

   PU L#11 (P#14)

  Package L#3 + L3 L#3 (4096KB)

 L2 L#6 (1024KB) + L1 L#6 (16KB) + Core L#6

   PU L#12 (P#3)

   PU L#13 (P#11)

 L2 L#7 (1024KB) + L1 L#7 (16KB) + Core L#7

   PU L#14 (P#7)

   PU L#15 (P#15)



Note that there is also an equivalent output in XML that is meant for exporting

/importing topologies but it is hardly readable to human-beings (see Importing

and exporting topologies from/to XML files for details).



On a 4-package 2-core Opteron NUMA machine (with two core cores disallowed by

the administrator), the lstopo tool may show the following graphical output

(with --disallowed for displaying disallowed objects):



[hagrid]



Here's the equivalent output in textual form:



Machine (32GB total)

  Package L#0

 NUMANode L#0 (P#0 8190MB)

 L2 L#0 (1024KB) + L1 L#0 (64KB) + Core L#0 + PU L#0 (P#0)

 L2 L#1 (1024KB) + L1 L#1 (64KB) + Core L#1 + PU L#1 (P#1)

  Package L#1

 NUMANode L#1 (P#1 8192MB)

 L2 L#2 (1024KB) + L1 L#2 (64KB) + Core L#2 + PU L#2 (P#2)

 L2 L#3 (1024KB) + L1 L#3 (64KB) + Core L#3 + PU L#3 (P#3)

  Package L#2

 NUMANode L#2 (P#2 8192MB)

 L2 L#4 (1024KB) + L1 L#4 (64KB) + Core L#4 + PU L#4 (P#4)

 L2 L#5 (1024KB) + L1 L#5 (64KB) + Core L#5 + PU L#5 (P#5)

  Package L#3

 NUMANode L#3 (P#3 8192MB)

 L2 L#6 (1024KB) + L1 L#6 (64KB) + Core L#6 + PU L#6 (P#6)

 L2 L#7 (1024KB) + L1 L#7 (64KB) + Core L#7 + PU L#7 (P#7)



On a 2-package quad-core Xeon (pre-Nehalem, with 2 dual-core dies into each

package):



[emmett]



Here's the same output in textual form:



Machine (total 16GB)

  NUMANode L#0 (P#0 16GB)

  Package L#0

 L2 L#0 (4096KB)

   L1 L#0 (32KB) + Core L#0 + PU L#0 (P#0)

   L1 L#1 (32KB) + Core L#1 + PU L#1 (P#4)

 L2 L#1 (4096KB)

   L1 L#2 (32KB) + Core L#2 + PU L#2 (P#2)

   L1 L#3 (32KB) + Core L#3 + PU L#3 (P#6)

  Package L#1

 L2 L#2 (4096KB)

   L1 L#4 (32KB) + Core L#4 + PU L#4 (P#1)

   L1 L#5 (32KB) + Core L#5 + PU L#5 (P#5)

 L2 L#3 (4096KB)

   L1 L#6 (32KB) + Core L#6 + PU L#6 (P#3)

   L1 L#7 (32KB) + Core L#7 + PU L#7 (P#7)



Programming Interface



The basic interface is available in hwloc.h. Some higher-level functions are

available in hwloc/helper.h to reduce the need to manually manipulate objects

and follow links between them. Documentation for all these is provided later in

this document. Developers may also want to look at hwloc/inlines.h which

contains the actual inline code of some hwloc.h routines, and at this document,

which provides good higher-level topology traversal examples.



To precisely define the vocabulary used by hwloc, a Terms and Definitions

section is available and should probably be read first.



Each hwloc object contains a cpuset describing the list of processing units

that it contains. These bitmaps may be used for CPU binding and Memory binding.

hwloc offers an extensive bitmap manipulation interface in hwloc/bitmap.h.



Moreover, hwloc also comes with additional helpers for interoperability with

several commonly used environments. See the Interoperability With Other

Software section for details.



The complete API documentation is available in a full set of HTML pages, man

pages, and self-contained PDF files (formatted for both both US letter and A4

formats) in the source tarball in doc/doxygen-doc/.



NOTE: If you are building the documentation from a Git clone, you will need to

have Doxygen and pdflatex installed -- the documentation will be built during

the normal "make" process. The documentation is installed during "make install"

to $prefix/share/doc/hwloc/ and your systems default man page tree (under

$prefix, of course).



Portability



Operating System have varying support for CPU and memory binding, e.g. while

some Operating Systems provide interfaces for all kinds of CPU and memory

bindings, some others provide only interfaces for a limited number of kinds of

CPU and memory binding, and some do not provide any binding interface at all.

Hwloc's binding functions would then simply return the ENOSYS error (Function

not implemented), meaning that the underlying Operating System does not provide

any interface for them. CPU binding and Memory binding provide more information

on which hwloc binding functions should be preferred because interfaces for

them are usually available on the supported Operating Systems.



Similarly, the ability of reporting topology information varies from one

platform to another. As shown in Command-line Examples, hwloc can obtain

information on a wide variety of hardware topologies. However, some platforms

and/or operating system versions will only report a subset of this information.

For example, on an PPC64-based system with 8 cores (each with 2 hardware

threads) running a default 2.6.18-based kernel from RHEL 5.4, hwloc is only

able to glean information about NUMA nodes and processor units (PUs). No

information about caches, packages, or cores is available.



Here's the graphical output from lstopo on this platform when Simultaneous

Multi-Threading (SMT) is enabled:



[ppc64-with]



And here's the graphical output from lstopo on this platform when SMT is

disabled:



[ppc64-with]



Notice that hwloc only sees half the PUs when SMT is disabled. PU L#6, for

example, seems to change location from NUMA node #0 to #1. In reality, no PUs

"moved" -- they were simply re-numbered when hwloc only saw half as many (see

also Logical index in Indexes and Sets). Hence, PU L#6 in the SMT-disabled

picture probably corresponds to PU L#12 in the SMT-enabled picture.



This same "PUs have disappeared" effect can be seen on other platforms -- even

platforms / OSs that provide much more information than the above PPC64 system.

This is an unfortunate side-effect of how operating systems report information

to hwloc.



Note that upgrading the Linux kernel on the same PPC64 system mentioned above

to 2.6.34, hwloc is able to discover all the topology information. The

following picture shows the entire topology layout when SMT is enabled:



[ppc64-full]



Developers using the hwloc API or XML output for portable applications should

therefore be extremely careful to not make any assumptions about the structure

of data that is returned. For example, per the above reported PPC topology, it

is not safe to assume that PUs will always be descendants of cores.



Additionally, future hardware may insert new topology elements that are not

available in this version of hwloc. Long-lived applications that are meant to

span multiple different hardware platforms should also be careful about making

structure assumptions. For example, a new element may someday exist between a

core and a PU.



API Example



The following small C example (available in the source tree as ``doc/examples/

hwloc-hello.c'') prints the topology of the machine and performs some thread

and memory binding. More examples are available in the doc/examples/ directory

of the source tree.



/* Example hwloc API program.

*

* See other examples under doc/examples/ in the source tree

* for more details.

*

* Copyright (c) 2009-2016 Inria. All rights reserved.

* Copyright (c) 2009-2011 Universit?eacute; Bordeaux

* Copyright (c) 2009-2010 Cisco Systems, Inc. All rights reserved.

* See COPYING in top-level directory.

*

* hwloc-hello.c

*/

#include "hwloc.h"

#include 

#include 

#include 

static void print_children(hwloc_topology_t topology, hwloc_obj_t obj,

int depth)

{

char type[32], attr[1024];

unsigned i;

hwloc_obj_type_snprintf(type, sizeof(type), obj, 0);

printf("%*s%s", 2*depth, "", type);

if (obj->os_index != (unsigned) -1)

printf("#%u", obj->os_index);

hwloc_obj_attr_snprintf(attr, sizeof(attr), obj, " ", 0);

if (*attr)

printf("(%s)", attr);

printf("\n");

for (i = 0; i < obj->arity; i++) {

print_children(topology, obj->children[i], depth + 1);

}

}

int main(void)

{

int depth;

unsigned i, n;

unsigned long size;

int levels;

char string[128];

int topodepth;

void *m;

hwloc_topology_t topology;

hwloc_cpuset_t cpuset;

hwloc_obj_t obj;

/* Allocate and initialize topology object. */

hwloc_topology_init(&topology);

/* ... Optionally, put detection configuration here to ignore

some objects types, define a synthetic topology, etc....

The default is to detect all the objects of the machine that

the caller is allowed to access. See Configure Topology

Detection. */

/* Perform the topology detection. */

hwloc_topology_load(topology);

/* Optionally, get some additional topology information

in case we need the topology depth later. */

topodepth = hwloc_topology_get_depth(topology);

/*****************************************************************

* First example:

* Walk the topology with an array style, from level 0 (always

* the system level) to the lowest level (always the proc level).

*****************************************************************/

for (depth = 0; depth < topodepth; depth++) {

printf("*** Objects at level %d\n", depth);

for (i = 0; i < hwloc_get_nbobjs_by_depth(topology, depth);

i++) {

hwloc_obj_type_snprintf(string, sizeof(string),

hwloc_get_obj_by_depth(topology, depth, i), 0);

printf("Index %u: %s\n", i, string);

}

}

/*****************************************************************

* Second example:

* Walk the topology with a tree style.

*****************************************************************/

printf("*** Printing overall tree\n");

print_children(topology, hwloc_get_root_obj(topology), 0);

/*****************************************************************

* Third example:

* Print the number of packages.

*****************************************************************/

depth = hwloc_get_type_depth(topology, HWLOC_OBJ_PACKAGE);

if (depth == HWLOC_TYPE_DEPTH_UNKNOWN) {

printf("*** The number of packages is unknown\n");

} else {

printf("*** %u package(s)\n",

hwloc_get_nbobjs_by_depth(topology, depth));

}

/*****************************************************************

* Fourth example:

* Compute the amount of cache that the first logical processor

* has above it.

*****************************************************************/

levels = 0;

size = 0;

for (obj = hwloc_get_obj_by_type(topology, HWLOC_OBJ_PU, 0);

obj;

obj = obj->parent)

if (hwloc_obj_type_is_cache(obj->type)) {

levels++;

size += obj->attr->cache.size;

}

printf("*** Logical processor 0 has %d caches totaling %luKB\n",

levels, size / 1024);

/*****************************************************************

* Fifth example:

* Bind to only one thread of the last core of the machine.

*

* First find out where cores are, or else smaller sets of CPUs if

* the OS doesn't have the notion of a "core".

*****************************************************************/

depth = hwloc_get_type_or_below_depth(topology, HWLOC_OBJ_CORE);

/* Get last core. */

obj = hwloc_get_obj_by_depth(topology, depth,

hwloc_get_nbobjs_by_depth(topology, depth) - 1);

if (obj) {

/* Get a copy of its cpuset that we may modify. */

cpuset = hwloc_bitmap_dup(obj->cpuset);

/* Get only one logical processor (in case the core is

SMT/hyper-threaded). */

hwloc_bitmap_singlify(cpuset);

/* And try to bind ourself there. */

if (hwloc_set_cpubind(topology, cpuset, 0)) {

char *str;

int error = errno;

hwloc_bitmap_asprintf(&str, obj->cpuset);

printf("Couldn't bind to cpuset %s: %s\n", str, strerror(error));

free(str);

}

/* Free our cpuset copy */

hwloc_bitmap_free(cpuset);

}

/*****************************************************************

* Sixth example:

* Allocate some memory on the last NUMA node, bind some existing

* memory to the last NUMA node.

*****************************************************************/

/* Get last node. There's always at least one. */

n = hwloc_get_nbobjs_by_type(topology, HWLOC_OBJ_NUMANODE);

obj = hwloc_get_obj_by_type(topology, HWLOC_OBJ_NUMANODE, n - 1);

size = 1024*1024;

m = hwloc_alloc_membind(topology, size, obj->nodeset,

HWLOC_MEMBIND_BIND, HWLOC_MEMBIND_BYNODESET);

hwloc_free(topology, m, size);

m = malloc(size);

hwloc_set_area_membind(topology, m, size, obj->nodeset,

HWLOC_MEMBIND_BIND, HWLOC_MEMBIND_BYNODESET);

free(m);

/* Destroy topology object. */

hwloc_topology_destroy(topology);

return 0;

}



hwloc provides a pkg-config executable to obtain relevant compiler and linker

flags. See Compiling software on top of hwloc's C API for details on building

program on top of hwloc's API using GNU Make or CMake.



On a machine 2 processor packages -- each package of which has two processing

cores -- the output from running hwloc-hello could be something like the

following:



shell$ ./hwloc-hello

*** Objects at level 0

Index 0: Machine

*** Objects at level 1

Index 0: Package#0

Index 1: Package#1

*** Objects at level 2

Index 0: Core#0

Index 1: Core#1

Index 2: Core#3

Index 3: Core#2

*** Objects at level 3

Index 0: PU#0

Index 1: PU#1

Index 2: PU#2

Index 3: PU#3

*** Printing overall tree

Machine

  Package#0

 Core#0

   PU#0

 Core#1

   PU#1

  Package#1

 Core#3

   PU#2

 Core#2

   PU#3

*** 2 package(s)

*** Logical processor 0 has 0 caches totaling 0KB

shell$



Questions and Bugs



Bugs should be reported in the tracker (https://github.com/open-mpi/hwloc/

issues). Opening a new issue automatically displays lots of hints about how to

debug and report issues.



Questions may be sent to the users or developers mailing lists (https://

www.open-mpi.org/community/lists/hwloc.php).



There is also a #hwloc IRC channel on Libera Chat (irc.libera.chat).



History / Credits



hwloc is the evolution and merger of the libtopology project and the Portable

Linux Processor Affinity (PLPA) (https://www.open-mpi.org/projects/plpa/)

project. Because of functional and ideological overlap, these two code bases

and ideas were merged and released under the name "hwloc" as an Open MPI

sub-project.



libtopology was initially developed by the Inria Runtime Team-Project. PLPA was

initially developed by the Open MPI development team as a sub-project. Both are

now deprecated in favor of hwloc, which is distributed as an Open MPI

sub-project.



See https://www.open-mpi.org/projects/hwloc/doc/ for more hwloc documentation,

actual links to related pages, images, etc.