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





On 2016-09-14 15:30, George Dunlap wrote:
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
Hi George,

I have always been using the default. I never had the need to set a specific device model. So it's qemu-upstream in my case.

Best regards,

Peter



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