By default, QEMU presents an IDE controller ( ide-hd or piix3-uhci) to XP. This provides maximum compatibility but terrible performance, as IDE lacks the queue depth capabilities of modern buses.
The Solution: VirtIO To achieve top performance, you must use the VirtIO paravirtualized drivers.
iostat -x 1 /var/lib/libvirt/images/windows.qcow2
Look for high await (anything >20ms indicates a problem) or %util near 100%.
Use these tools inside the Windows guest:
