[Bug 1915811] Re: Empty NUMA topology in machines with high number of CPUs

[Brian Murray]

Hello Victor, or anyone else affected,

Accepted libvirt into bionic-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/libvirt/4.0.0-1ubuntu8.19 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
bionic to verification-done-bionic. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-bionic. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: libvirt (Ubuntu Bionic)
       Status: New => Fix Committed

** Tags added: verification-needed-bionic

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https://bugs.launchpad.net/bugs/1915811

Title:
  Empty NUMA topology in machines with high number of CPUs

Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive stein series:
  Fix Committed
Status in Ubuntu Cloud Archive train series:
  Fix Committed
Status in Ubuntu Cloud Archive ussuri series:
  Fix Committed
Status in libvirt package in Ubuntu:
  Fix Released
Status in libvirt source package in Xenial:
  Fix Committed
Status in libvirt source package in Bionic:
  Fix Committed
Status in libvirt source package in Focal:
  Fix Committed
Status in libvirt source package in Groovy:
  Fix Committed

Bug description:
  [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.

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