The default USB controller of pc machine type

[Han Han]

On Wed, Jul 13, 2022 at 7:04 PM Daniel P. Berrangé <berrange at redhat.com>
wrote:

> On Wed, Jul 13, 2022 at 07:00:17PM +0800, Han Han wrote:
> > 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.
>
> A qemu-xhci controller can be added to any x86 machien type regardless
> of the default, and most mgmt apps will do exactly that.
>

Does that mean, the default USB controller for a specific x86 machine type
does NOT matter?
And leave the default USB controller to up-layer mgmt apps?

>
> With regards,
> Daniel
> --
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