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hwloc-distances - Displays distance matrices


hwloc-distances [options]


Display hwloc logical indexes (default) instead of physical/OS indexes.
Display OS/physical indexes instead of hwloc logical indexes.
Read topology from XML file <file> (instead of discovering the topology on the local machine). If <file> is "-", the standard input is used. XML support must have been compiled in to hwloc for this option to be usable.
Read topology from the chroot specified by <directory> (instead of discovering the topology on the local machine). This option is generally only available on Linux. The chroot was usually created by gathering another machine topology with hwloc-gather-topology.
Simulate a fake hierarchy (instead of discovering the topology on the local machine). If <specification> is "node:2 pu:3", the topology will contain two NUMA nodes with 3 processing units in each of them. The <specification> string must end with a number of PUs.
Enforce the input in the given format, among xml, fsroot and synthetic.
Restrict the topology to the given cpuset.
Do not consider administration limitations.
Verbose messages.
Report version and exit.


hwloc-distances displays also distance matrices attached to the topology. The value in the i-th row and j-th column is the distance from object #i to object #j.

Unless defined by the user, matrices currently always contain relative latencies between NUMA nodes (which may or may not be accurate). See the definition of struct hwloc_distances_s in include/hwloc.h or the documentation for details.

These latencies are normalized to the latency of a local (non-NUMA) access. Hence 3.5 in row #i column #j means that the latency from cores in NUMA node #i to memory in NUMA node #j is 3.5 higher than the latency from cores to their local memory. A breadth-first traversal of the topology is performed starting from the root to find all distance matrices.

NOTE: lstopo may also display distance matrices in its verbose textual output. However lstopo only prints matrices that cover the entire topology while hwloc-distances also displays matrices that ignore part of the topology.


On a quad-package opteron machine:

$ hwloc-distances
Latency matrix between 4 NUMANodes (depth 2) by logical indexes:
index 0 1 2 3
0 1.000 1.600 2.200 2.200
1 1.600 1.000 2.200 2.200
2 2.200 2.200 1.000 1.600
3 2.200 2.200 1.600 1.000


Upon successful execution, hwloc-distances returns 0.

hwloc-distances will return nonzero if any kind of error occurs, such as (but not limited to) failure to parse the command line.


hwloc(7), lstopo(1)

April 27, 2017 1.11.7