live migration failed no CPU model specified

[Eli Qiao]

1" threads="1"/>\n</cpu>\n',) from (pid=2305) to_xml /opt/stack/nova/nova/virt/libvirt/config.py:82
<cpu match="exact">
  <topology sockets="1" cores="1" threads="1"/>
</cpu>

2015-03-19 15:35:37.697 DEBUG nova.virt.libvirt.config [req-b2abf15d-cb2c-4af9-8356-181e16ee091a admin admin] Generated XML ('<cpu match="exact">\n <topology sockets="1" cores="1" threads="1"/>\n</cpu>\n',) from (pid=2305) to_xml /opt/stack/nova/nova/virt/libvirt/config.py:82
2015-03-19 15:35:37.699 ERROR nova.virt.libvirt.driver [req-b2abf15d-cb2c-4af9-8356-181e16ee091a admin admin] CPU doesn't have compatibility.

Requested operation is not valid: no CPU model specified

Refer to http://libvirt.org/html/libvirt-libvirt-host.html#virCPUCompareResult
2015-03-19 15:35:37.702 DEBUG oslo_messaging._drivers.amqpdriver [req-b2abf15d-cb2c-4af9-8356-181e16ee091a admin admin] MSG_ID is 374d071984dd497ba58b9c0fe6ad0ea1 from (pid=2305) _send /usr/local/lib/python2.7/dist-packages/oslo_messaging/_drivers/amqpdriver.py:310
2015-03-19 15:35:37.702 DEBUG oslo_messaging._drivers.amqp [req-b2abf15d-cb2c-4af9-8356-181e16ee091a admin admin] UNIQUE_ID is f11d04094b1d4614b06a17fe7ffe3fae. from (pid=2305) _add_unique_id /usr/local/lib/python2.7/dist-packages/oslo_messaging/_drivers/amqp.py:226
2015-03-19 15:35:37.747 ERROR oslo_messaging.rpc.dispatcher [req-b2abf15d-cb2c-4af9-8356-181e16ee091a admin admin] Exception during message handling: Migration pre-check error: CPU doesn't have compatibility.

Requested operation is not valid: no CPU model specified

[Eli Qiao (taget-9)]

in nova.conf

[libvirt]
cpu_mode = none
virt_type = kvm

by checking libvirt driver

    def _get_guest_cpu_model_config(self):
        mode = CONF.libvirt.cpu_mode
        model = CONF.libvirt.cpu_model

        if (CONF.libvirt.virt_type == "kvm" or
            CONF.libvirt.virt_type == "qemu"):
            if mode is None:
                mode = "host-model"
            if mode == "none":
                return vconfig.LibvirtConfigGuestCPU()

if mode is set to none, then return vconfig.LibvirtConfigGuestCPU()
but it doesn't has cpu_model at all.

[Joe Gordon (jogo)]

I am not sure this is actually valid, if you are live migrating across two different types of CPUs, you will get this error.

[Markus Zoeller (markus_z) (mzoeller)]

I made the same observation on a setup where both nodes have the same
CPU type. The missing <model> element causes an XML parser error.

    $ cat cpu_without_model.xml
    <cpu match="exact">
     <topology sockets="1" cores="1" threads="1"/>
    </cpu>
    $ virsh cpu-compare cpu_without_model.xml
    error: Failed to compare host CPU with cpu_without_model.xml
    error: Requested operation is not valid: no CPU model specified

The model is not saved in the database [1]. But this database entry is
loaded into the "instance.vcpu_model" property and used to query the
cpu [2]:

    def check_can_live_migrate_destination([...]):
        [...]
        if not instance.vcpu_model:
            [...]
        else:
            self._compare_cpu(instance.vcpu_model, None)

    def _compare_cpu(self, guest_cpu, host_cpu_str):
        [...]

        if guest_cpu is None:
            [...]
        else:
            cpu = self._vcpu_model_to_cpu_config(guest_cpu)

The VirtCPUModel was introduced with [3] but I don't know if this
introduced the described issue.

[1] http://paste.openstack.org/show/193858/
[2] https://github.com/openstack/nova/blob/master/nova/virt/libvirt/driver.py
[3] Gerrit; Add VirtCPUModel nova objects;
    https://review.openstack.org/#/c/148138/

[Markus Zoeller (markus_z) (mzoeller)]

It seems that this issue was also discovered by Tony Walker in https://bugs.launchpad.net/nova/+bug/1082414/comments/29

His patch set seems to solve the problem: https://review.openstack.org/#/c/161944/2