hwloc-distances man page

hwloc-distances — Displays distance matrices


hwloc-distances [options]


-l --logical
Display hwloc logical indexes (default) instead of physical/OS indexes.
-p --physical
Display OS/physical indexes instead of hwloc logical indexes.
-i <file>, --input <file>
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.
-i <directory>, --input <directory>
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.
-i <specification>, --input <specification>
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.
--if <format>, --input-format <format>
Enforce the input in the given format, among xml, fsroot and synthetic.
--restrict <cpuset>
Restrict the topology to the given cpuset.
Do not consider administration limitations.
-v --verbose
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

Return Value

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.

See Also

hwloc(7), lstopo(1)


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