Should APIC be used on VMs?

Solution 1:

It's 2013 and there's virtually no good reason to disable APIC, and plenty of good reason to enable it.

This may not have been true 15 years ago when APIC was new and not well implemented by various hardware vendors, but that hasn't been the case for a very long time.

Microsoft's explanation (from 2003!) is probably the best I can give you, and I'm surprised you didn't find it since it was linked from Wikipedia's page on APIC.

In essence, APIC is a dramatic improvement over the old PC interrupt system which dates back to the 1980s, allowing for more interrupts and less interrupt sharing. This translates into better performance and the ability to use more peripheral devices, both of which are true whether the machine is physical or virtual.

Rule of thumb is: APIC should always be enabled unless there's a specific reason to disable it, such as using ancient hardware, or virtualizing an old NT/2000 system with a non-APIC HAL.