There are use cases where setting multiple queues per vnic makes sense (e.g running two multi-vcpu heavily-intercommunicating VMs on the same host).

Setting multiple queues has a (minor) side effect of wasting host memory.

This RFE tracks a request to have a smarter policy of setting the number of queues: we'd like to make it equal to the number of vcpu, unless another number is requested by the VM admin.

Queues should be set only on virtio vnics; in particular, they should not set on passed-through vnics.


http://libvirt.org/formatdomain.html#elementsDriverBackendOptions

queues
    The optional queues attribute controls the number of queues to be used for either Multiqueue virtio-net or vhost-user network interfaces. Use of multiple packet processing queues requires the interface having the <model type='virtio'/> element. Each queue will potentially be handled by a different processor, resulting in much higher throughput. virtio-net since 1.0.6 (QEMU and KVM only) vhost-user since 1.2.17 (QEMU and KVM only)