Re: USB Passthrough 1.1 performance problem...

[Erik Brakkee <erik@brakkee.org>]

Erik Brakkee wrote:
> Hi,
>
>
> I am using a tv card in a VM and get jerky video.As I understand it, 
> the VM is using USB 1.1. However, when I set the USB controller in the 
> BIOS of my server to Fullspeed (12 Mbit/s) which is the USB 1.1 speed 
> I am able to get perfect results on the host but still on the guest 
> the video is jerky.
>
> Are there some tuning parameters I can use or perhaps even kernel 
> configuration paramters on the host to solve this?
>
> Cheers
>   Erik
>
> Host:    Motherboard Supermicro X8DTi-F, Intel Xeon L5630, 12MB
>              OS: Opensuse 11.3 64 bit
>
> Guest:   OS: Opensuse 11.3 64 bit
I can say now that I am giving up on getting this to work. One 
alternative was to use PCI passthrough the USB hardware,  but that 
didn't work for the USB that was on the motherboard. So I bought a USB 
PCI card and tried to use PCI passthrough for that. Unfortunately other 
problems occured there.

For one, the problem with 4K alignment. But I could fix that by using 
the pci=resource_alignment=... kernel parameter. In my grub/menu.lst it 
says:

    kernel /vmlinuz-2.6.34.7-0.5-default root=/dev/hsystem/root quiet
    showopts intel_iommu=on
    pci=resource_alignment=01:04.0;01:04.1;01:04.2 noirqdebug vga=0x31a


The noirqdebug flas was needed to avoid the host from disabling the IRQ 
(it was a shared IRQ).

Using this, I could configure PCI passthrough and start the VM. Also the 
USB device showed up there. Only it did not work at all.

Here is a summary of my journey up until know:

The original approach I wanted to use was to pass my old PCI card (WinTV 
PVR-500) to a VM. This card is a well supported card and has been doing 
fine for me. Because of the PCI passthrough problems with the wintv 
card, I decided to try a USB card instead. This gave me a 'ctrl buffer 
too small' issue that I could solve by taking the source RPM for kvm and 
applying a known patch from red hat (increasing buffer size from 2048 to 
8192). But then I got jerky video, probably due to USB 1.1 issues. To 
bypass these I could use PCI passthrough for USB. But with the PCI 
passthrough of this card I am again running into issues probably related 
to Shared IRQs. So, after all this I am back to square one.

I have now modified my approach so instead of running a separate minimal 
host with my old server as a guest, I am now running the old server 
(same install) on the new hardware, using it as a host. I would 
definitely be interested in trying this out further in the future. I 
even tried Xen for a brief moment, only to realize that my host and 
guest felt slower (slower startup and execution) and much more difficult 
to handle.

 From the experience of the last two days fulltime trying to get things 
working I can only conclude that the following two features would be 
really important to have:

    * Extended PCI passthrough support
          o shared IRQ support
          o supporting cases where memory is not aligned on a 4K boundary
    * USB passthrough
          o support USB 2.0
          o support USB 3.0 (but taking one step at a time, 2.0 would
            also be great).

 From the above, PCI passthrough improvements are most important as they 
will also allow (cheap) workarounds for USB passthrough issues.

I am definitely interested in hearing about new releases from KVM. Is 
there a mailing list I should subscribe to get information about the 
latest releases without intermediate discussions? I would also be 
interested in using latest stable versions of KVM for opensuse. Is there 
any repository I can configure to get those?

Cheers
   Erik