When using calico, the vif_type is tap, therefore when the instance is being created, the method plug_tap() is invoked, which creates the tap device prior to launching the instance.

That tap device is currently always created without multiqueue as per [1]. When libvirt creates the instance, the XML definition "queues=<x>" clashes with the fact that the pre-existing tap interface doesn't have multiqueue enabled, and therefore errors out with the exception below. The code at [2] already handles multiqueue, but it is never invoked with multiqueue=True.

Alternatively, as a current workaround, if the instance is shutdown through virsh, or rebooted through nova, it causes the tap device to be removed, to be created again by libvirt instead, allowing the tap device to be set up with multiqueue appropriately if its XML is manually edited. This begs the question as why the plug_tap() method needs to pre-create the interface at all, if when the VM rebooted libvirt does so regardless of plug_tap().

Steps to reproduce:

1) Ubuntu bionic + devstack master + follow instructions at [3]
2) wget https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img
3) openstack image create bionic-mq --file bionic-server-cloudimg-amd64.img --property hw_vif_multiqueue_enabled=True
4) openstack image create bionic --file bionic-server-cloudimg-amd64.img
5) ssh-keygen
6) openstack keypair create key1 --public-key ~/.ssh/id_rsa.pub
7) openstack flavor create --vcpu 2 --ram 1024 --disk 10 --public --id 10 test_flavor
8) openstack server create --network calico --flavor test_flavor --image bionic --key-name key1 no-mq

instance is created successfully

9) ip a

6: tapcc353751-13: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000

10) sudo virsh edit 1

add "<driver name='vhost' queues='2'/>" to the interface section

11) openstack server reboot no-mq

wait a few secs

12) ip a

7: tapcc353751-13: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UNKNOWN group default qlen 1000

13) ssh to the instance and run "sudo ethtool -l <interface>"

Combined:       2

14) openstack server delete no-mq

15) openstack server create --network calico --flavor test_flavor --image bionic-mq --key-name key1 mq

instance fails to be created, log shows the below stack trace.


[1] https://github.com/openstack/nova/blob/f521f4dbace0e35bedd089369da6f6969da5ca32/nova/virt/libvirt/vif.py#L701
[2] https://github.com/openstack/nova/blob/f521f4dbace0e35bedd089369da6f6969da5ca32/nova/privsep/linux_net.py#L109
[3] https://docs.projectcalico.org/getting-started/openstack/installation/devstack

Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [None req-71d40776-0fa7-466e-9060-11472b5bce42 admin admin] [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4] Instance failed to spawn: libvirt.libvirtError: Unable to create tap device tapb6021dd0-fd: Invalid argument
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4] Traceback (most recent call last):
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/compute/manager.py", line 2628, in _build_resources
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     yield resources
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/compute/manager.py", line 2401, in _build_and_run_instance
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     accel_info=accel_info)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 3701, in spawn
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     cleanup_instance_disks=created_disks)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 6700, in _create_guest_with_network
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     cleanup_instance_disks=cleanup_instance_disks)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     self.force_reraise()
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     six.reraise(self.type_, self.value, self.tb)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/six.py", line 703, in reraise
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     raise value
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 6669, in _create_guest_with_network
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     post_xml_callback=post_xml_callback)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 6599, in _create_guest
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     guest.launch(pause=pause)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/virt/libvirt/guest.py", line 160, in launch
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     self._encoded_xml, errors='ignore')
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     self.force_reraise()
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     six.reraise(self.type_, self.value, self.tb)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/six.py", line 703, in reraise
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     raise value
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/opt/stack/nova/nova/virt/libvirt/guest.py", line 155, in launch
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     return self._domain.createWithFlags(flags)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/eventlet/tpool.py", line 190, in doit
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     result = proxy_call(self._autowrap, f, *args, **kwargs)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/eventlet/tpool.py", line 148, in proxy_call
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     rv = execute(f, *args, **kwargs)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/eventlet/tpool.py", line 129, in execute
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     six.reraise(c, e, tb)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/six.py", line 703, in reraise
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     raise value
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/eventlet/tpool.py", line 83, in tworker
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     rv = meth(*args, **kwargs)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]   File "/usr/local/lib/python3.6/dist-packages/libvirt.py", line 1098, in createWithFlags
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4]     if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4] libvirt.libvirtError: Unable to create tap device tapb6021dd0-fd: Invalid argument
Aug 27 18:58:38 devstack nova-compute[7968]: ERROR nova.compute.manager [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4] 
Aug 27 18:58:38 devstack nova-compute[7968]: INFO nova.compute.manager [None req-71d40776-0fa7-466e-9060-11472b5bce42 admin admin] [instance: 69a0a527-9c33-432f-8889-c421ae8aebb4] Terminating instance