I have migrated KVM VMs from a CentOS 6 to a CentOS 7 host. All work fine post-migration, CentOS 3 (don't ask ...), CentOS 6, CentOS 7, Windows. But the CentOS 5 VMs failed. At some point during the boot process, they became unpingable and also inaccessible. I have correlated this to the start of the irqbalance service and was wondering if it is generally considered best practice to turn it off. The VMs in question all have at least 2 vcpus, and the C5 VMs are the odd ones out.