Hello,
I found that the default USB controller for q35 machine type is qemu-xhci
while for pc it is piix3-uhci. Here are the results(on qemu-kvm-7.0.0
qemu-kvm-7.0.0):
➜ ~ cat /tmp/usb.xml
<domain type="kvm">
<name>USB</name>
<uuid>1a81d4ef-6537-4ae8-b257-8a15e0c0525f</uuid>
<memory>2097152</memory>
<currentMemory>2097152</currentMemory>
<vcpu>1</vcpu>
<os>
<type arch="x86_64" machine="q35">hvm</type>
<boot dev="hd"/>
</os>
<devices>
<emulator>/usr/libexec/qemu-kvm</emulator>
</devices>
</domain>
➜ ~ virsh define /tmp/usb.xml && virsh dumpxml USB|grep usb
Domain 'USB' defined from /tmp/usb.xml
<controller type='usb' index='0' model='qemu-xhci'>
➜ ~ cat /tmp/usb-pc.xml
<domain type="kvm">
<name>USB</name>
<uuid>1a81d4ef-6537-4ae8-b257-8a15e0c0525f</uuid>
<memory>2097152</memory>
<currentMemory>2097152</currentMemory>
<vcpu>1</vcpu>
<os>
<type arch="x86_64" machine="pc">hvm</type>
<boot dev="hd"/>
</os>
<devices>
<emulator>/usr/libexec/qemu-kvm</emulator>
</devices>
</domain>
➜ ~ virsh define /tmp/usb-pc.xml && virsh dumpxml USB|grep usb
Domain 'USB' defined from /tmp/usb-pc.xml
<controller type='usb' index='0' model='piix3-uhci'>
And the default usb controller for q35 has been added since:
ed2049ea19 qemu: auto-add generic xhci rather than NEC xhci to Q35 domains
As I know, pc machine supports qemu-xhci as well. Morever, the
performance of qemu-xhci is better than piix3-uhci. So why not update the
default usb controller of pc machine type to qemu-xhci? I think we can
improve it here.