[Openstack-operators] Libvirt CPU map (host-model)
moreira.belmiro.email.lists at gmail.com
Tue Oct 10 12:18:21 UTC 2017
yes, this is exactly what we are observing.
Thanks for the bugzilla pointer.
We now also opened a ticket through the RedHat support.
On Mon, Oct 9, 2017 at 12:37 PM, Paul Browne <pfb29 at cam.ac.uk> wrote:
> Hello Belmiro,
> We ran into this issue recently, similarly upgrading a RHEL7.3 OpenStack
> Platform Overcloud to RHEL7.4 and in the process upgrading libvirtd.
> For instances that were spawned prior to this upgrade, we see the CPU
> flags  , but for new instance workload the CPU flags . Notably the
> CMT=disabled flag is present in  but absent in 
> This similarly prevents live migration of the older spawned instances, as
> the CMT=disabled flag is rejected.
> A RH bugzilla  was opened on the issue which attracted a lot of really
> good contributions from libvirt maintainers. The one sure-fire workaround
> we'd found is just to cold-boot the instance again, starting it under the
> new libvirtd. But from that BZ there is also a slightly more hack-ish
> workaround to hand-edit the running domain XML and clear the offending CMT
> flag (comment 12 on that BZ).
> Hope this helps some,
> Paul Browne
>  https://pastebin.com/JshWi6i3
>  https://pastebin.com/5b8cAanP
>  https://bugzilla.redhat.com/show_bug.cgi?id=1495171
> On 9 October 2017 at 04:59, Belmiro Moreira <moreira.belmiro.email.lists@
> gmail.com> wrote:
>> the CPU model that we expose to the guest VMs varies considering the
>> compute node use case.
>> We use "cpu_mode=host-passthrough" for the compute nodes that run batch
>> processing VMs and "cpu_mode=host-model" for the compute nodes for service
>> VMs. The reason to have "cpu_mode=host-model" is because we assumed that
>> new CPUs (in the libvirt map) will continue to support previous features
>> allowing for live migration when we need to move the VMs to a new CPU
>> We recently upgraded from CentOS7.3 (libvirt 2.0.0) to CentOS7.4 (libvirt
>> 3.2.0) and noticed that now libvirt maps a slightly different CPU for the
>> guests. For example, still "Haswell no-TSX" but no mention to the feature
>> "cmt". This blocks suspended VMs to restore and live migrate.
>> Has anyone experienced this same problem?
>> We are thinking in few solutions but none of them are nice (downgrade
>> libvirt? hard reboot instances? ...)
>> OpenStack-operators mailing list
>> OpenStack-operators at lists.openstack.org
> Paul Browne
> Research Computing Platforms
> University Information Services
> Roger Needham Building
> JJ Thompson Avenue
> University of Cambridge
> United Kingdom
> E-Mail: pfb29 at cam.ac.uk
> Tel: 0044-1223-746548
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