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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.09.16 at 16:04, <miles@xxxxxxxx> wrote:
> On 2016-09-14 14:50, Jan Beulich wrote:
>>>>> On 14.09.16 at 13:34, <george.dunlap@xxxxxxxxxx> wrote:
>>> 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?
> 
> 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.

Looks wrong in any case, but I have no clue whether it's indicative
of the problem you're having. In any event in the qemu tree in
hw/xen/xen_pt.h there's an "#ifdef XEN_PT_LOGGING_ENABLED"
conditional close to the top. Could you make this "#if 1" instead
(or simply #define XEN_PT_LOGGING_ENABLED in the line above)
and re-build at least qemu? The log of a subsequent guest run
should then be quite a bit more helpful in possibly spotting what's
going wrong to cause those messages.

And then it's of course rather relevant to know what device 00:06.0
actually is (iirc these are guest BDF values), considering that you're
passing through more than one.

Jan



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