Public bug reported:
[impact]
libvirt fails to populate its NUMA topology when the machine has a large
number of CPUs assigned to a single node. This happens when the number
of CPUs fills the bitmask (all to one), hitting a workaround introduced
to build the NUMA topology on machines that have non contiguous node
ids. This has been already fixed upstream in the commits listed below.
[scope]
The fix is needed for Xenial, Bionic, Focal and Groovy.
It's fixed upstream with commits 24d7d85208 and 551fb778f5 which are
included in v6.8, so both are already in hirsute.
[test case]
On a machine like the EPYC 7702P, after setting the NUMA config to NPS1
(single node per processor), or just a VM with 128 CPUs, "virsh
capabilities" does not show the NUMA topology:
# virsh capabilities | xmllint --xpath '/capabilities/host/topology' -
<topology>
<cells num="0">
</cells>
</topology>
When it should show (edited to shorten the description):
<topology>
<cells num="1">
<cell id="0">
<memory unit="KiB">5027820</memory>
<pages unit="KiB" size="4">1256955</pages>
<pages unit="KiB" size="2048">0</pages>
<distances>
<sibling id="0" value="10"/>
</distances>
<cpus num="128">
<cpu id="0" socket_id="0" core_id="0" siblings="0"/>
....
<cpu id="127" socket_id="127" core_id="0" siblings="127"/>
</cpus>
</cell>
</cells>
</topology>
[Where problems could occur]
Any regression would likely involve a misconstruction of the NUMA
topology, in particular for machines with non contiguous node ids.
** Affects: libvirt (Ubuntu)
Importance: Undecided
Status: New
** Tags: sts
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https://bugs.launchpad.net/bugs/1915811
Title:
Empty NUMA topology in machines with high number of CPUs
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