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

[Peter Milesson <miles@xxxxxxxx>]

On 2016-09-14 14:50, 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?
>
> Jan
Hi Jan,

No, I did not try a debug build. However, the system seems fairly stable 
now, only the display driver crashing once, or twice a day. That did 
occur with Xen 4.6.3 also, but maybe once a week. Looking at the log 
files, I cannot see anything particular that stands out, except for the 
domU log.
The domU log file qemu-dm-<Name>.log started to contain the following 
lines after upgrading to 4.7:
[00:06.0] xen_pt_bar_read: Error: Should not read BAR through QEMU. 
@0x0000000000000004
[00:06.0] xen_pt_bar_write: Error: Should not write BAR through QEMU. 
@0x0000000000000000
There are only a couple of lines with write, the rest with read. I don't 
know what significance it's got, but there are around 350 lines every day.
Thanks a lot for your interest and good work.

Regards,

Peter




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