---
name: "hwloc-diff"
section: "1"
platform: "linux"
package: "hwloc"
version: "2.15.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/hwloc-diff"
---

# hwloc-diff(1)

Compute differences between two XML topologies

## NAME

hwloc-diff - Compute differences between two XML topologies

## SYNOPSIS

**hwloc-diff** \[*options*\] *\<input1.xml\>* *\<input2.xml\>*

**hwloc-diff** \[*options*\] *\<input1.xml\>* *\<input2.xml\>* *\<output.xml\>*

## OPTIONS

- **--refname** \<name\>

  Use \<name\> as the identifier for the reference topology in the output XML difference. It is meant to tell which topology should be used when applying the resulting difference. hwloc-patch may use that name to automatically load the relevant reference topology XML. By default, \<input1.xml\> is used without its full path.

- **--version**

  Report version and exit.

- **-h** **--help**

  Display help message and exit.

## DESCRIPTION

hwloc-diff computes the difference between two XML topologies and stores the result into \<output.xml\> if any, or dumps it to stdout otherwise.

The output difference may later be applied to another topology with hwloc-patch.

hwloc-compress-dir may be used for computing the diffs between all XML files in a directory.

**NOTE:** If some application-specific userdata were been exported to the input XMLs, they will be ignored and discarded from the output because hwloc has no way to understand and compare them.

**NOTE:** It is highly recommended that you read the [hwloc(7)](/hwloc/7.md) overview page before reading this man page.  Most of the concepts described in [hwloc(7)](/hwloc/7.md) directly apply to the hwloc-diff utility.

## EXAMPLES

hwloc-diff's operation is best described through several examples.

Compute the difference between two XML topologies and output it to stdout:

    $ hwloc-diff fourmi023.xml fourmi024.xml\
     Found 11 differences, exporting to stdout\
     \<?xml version="1.0" encoding="UTF-8"?\>\
     ...

Output the difference to file diff.xml instead:

    $ hwloc-diff fourmi023.xml fourmi024.xml diff.xml\
     Found 11 differences, exporting to diff.xml

When the difference is too complex to be represented:

    $ hwloc-diff fourmi023.xml avakas-frontend1.xml\
     Found 1 differences, including 1 too complex ones.\
     Cannot export differences to stdout

Directly compute the difference between two topologies and apply it to another one:

    $ hwloc-diff fourmi023.xml fourmi024.xml \| hwloc-patch fourmi025.xml -

## RETURN VALUE

Upon successful execution, hwloc-diff outputs the difference. The return value is 0.

If the difference is too complex to be represented, an error is returned and the output is not generated.

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

## SEE ALSO

[hwloc(7)](/hwloc/7.md), [lstopo(1)](/lstopo/1.md), [hwloc-patch(1)](/hwloc-patch/1.md), [hwloc-compress-dir(1)](/hwloc-compress-dir/1.md)