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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

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

~Andrew

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