On Mon, 2016-11-07 at 14:50 -0500, Laine Stump wrote:
Previously we added a set of EHCI+UHCI controllers to Q35 machines to mimic real hardware as closely as possible, but recent discussions have pointed out that the nec-usb-xhci (USB3) controller is much more virtualization-friendly (uses less CPU), so this patch switches the default for Q35 machinetypes to add an XHCI instead (if it's supported, which it of course *will* be). Since none of the existing test cases left out USB controllers in the input XML, a new Q35 test case was added which has *no* devices, so ends up with only the defaults always put in by qemu, plus those added by libvirt.
We should probably have added that test case a while ago :) ACK -- Andrea Bolognani / Red Hat / Virtualization