Re: [Xen-users] Xen 4.7.0 graphics pass through problems (Win10, AMD Radeon)

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 14/09/16 14:23, Andrew Cooper wrote:
> On 14/09/16 13:50, Jan Beulich wrote:
>>>>> On 14.09.16 at 13:34, <george.dunlap@xxxxxxxxxx> wrote:
>>>>  On 2016-09-09 09:51, Peter Milesson wrote:
>>> [snip]
>>>>> I've been using Xen for 3 years, starting out with 4.2, and I've been
>>>>> upgrading regularly, and installed 4.7.0 today.
>>>>>
>>>>> I'm using Windows 10, 64-bit with PCI pass through in a VM with
>>>>> PV-drivers, using a AMD Radeon HD6450 card (AMD graphics cards don't seem 
>>>>> to
>>>>> need graphics pass through)
>>>>>
>>>>> Previously (up till Xen 4.6.3), the graphics output has displayed some
>>>>> shorter lines, a bit like thin coarse snow, when watching videos. The
>>>>> distortions stayed within the movie, and was tolerable.
>>>>>
>>>>> After upgrade to Xen 4.7.0, the video performance is seriously ugly. Just
>>>>> for example, I open cnn.com and move the mouse pointer up and down over 
>>>>> the
>>>>> photos, which creates a bunch of flickering lines over the display. The 
>>>>> same
>>>>> with moving content in Youtube for example. Or opening a Cygwin terminal
>>>>> window and scrolling through a file. Terrible.
>>>>>
>>>>> Nothing else has changed, only the Xen version.
>>> [snip]
>>>
>>> On Fri, Sep 9, 2016 at 10:35 AM, Peter Milesson <miles@xxxxxxxx> wrote:
>>>> Hi again,
>>>>
>>>> I've been playing around a bit more.
>>>>
>>>> It seems one of the problems is that I passed a couple of PCI-devices (USB
>>>> controllers) to the VM, beside the graphics card.
>>>>
>>>> When I pass the USB-devices individually in the VM configuration file
>>>> (usbdevice=['tablet','host:1.4','host:1:9','host:x.y']), the display
>>>> problems seem to be more or less gone.
>>> Jan / Andy,
>>>
>>> Can you think of anything that's changed between 4.6 and 4.7 that
>>> would cause the performance problems he's describing when both a video
>>> card and a usb controller are passed through, but not when only the
>>> video card is passed through?
>> Not really, no. Peter - are there any indications of problems in
>> one or more of the logs (Xen, xl, qemu)? Did you try running a
>> debug build of all Xen components?
> 
> Furthermore, does "Nothing else has changed, only the Xen version." mean
> switching your distro packages between two versions of xen, or literally
> only switching the hypervisor itself.

I assume he's using "Xen" to mean the whole Xen system -- hypervisor +
tools + qemu.

> A substantial quantity of the complexity here is in qemu, rather than Xen.

Rather than the hypervisor, you mean.

Another thing worth asking, Peter: Have you tried running with
qemu-traditional (by adding the line below to your config file) rather
than qemu-upstream, to see if that makes a difference?

device_model_version="qemu-xen-traditional"

qemu-traditional almost ever changes, so if it worked better, then that
would point the finger at changes in qemu (at which point we would have
to bring in a different set of people to help diagnose it).

 -George

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