[Qemu-devel] Re: [PATCH 0/5] Various USB fixes and improvements

[Anthony Liguori <anthony@codemonkey.ws>]

Max Krasnyansky wrote:
> This patch series started when I tried to share USB ports between 
> four instances of Windows XP running on the same Linux box (under KVM).
> I quickly realized that current USB support is not very flexible. We do
> not handle devices disconnects, there is not way to assign certain USB
> ports to VM instance, etc.
>
> Once I fixed that I discovered that USB devices that I absolutely need
> in the VMs (Xilinx and Altera USB dongles) do not really work with
> QEMU. VMs were getting stuck, applications unhappy, etc.
> So I endded up rewriting UHCI and Linux host USB layers to make them 
> fully async and to support multiple outstanding transactions.
>
> The result is quite nice. We can now assign USB buses to VM instances 
> and devices are automatically connected to the VMs. Just do 
>     usb_add host:N.*
> in the console or -usbdevice command line option (N is the bus number).
> Also when device is disconnected from the host it's automatically removed
> from the guest.
>
> Host USB devices operate in fully async mode (except the control transfers).
> All the stalls and jerkiness due to long synchronous transactions is gone.
> I can easily hook up four different USB devices (mouse, CF card reader, 
> phone, Xilinx dongle) and everything is working perfectly. Mouse movements
> are silky smooth :).
>
> I did some profiling with OProfile and we seems to be doing ok while XP is 
> pumping ~10 MBytes over USB (reported by one of the apps I'm using). UHCI 
> stuff is well below VNC for example.
>
> There is more work to be done (async control transfers for example). But I 
> think this is way better than what we have now and is ready for more testing
> by wider audience. 
>
> Most of the testing so far was done with KVM flavor of QEMU. I did test 
> generic i386-softmmu target a bit, it's too slow for any serious testing 
> with XP. I did full compile (all targets) too and it went fine.
>   

Altogether this patch series looks very promising.  The current USB pass 
through code is pretty fickle so some clean-up is definitely needed.

I don't understand USB well enough to do a thorough review.  I hope 
others can look through it and provide more detailed feedback.  I'll do 
some testing of it tonight.

Regards,

Anthony Liguori