Re: [Xen-devel] VGA passthrough and AMD drivers

[Mats Petersson <mats.petersson@xxxxxxxxxx>]

On 07/12/12 14:12, Aurélien MILLIAT wrote:
> Hi all,
>
> I have made some tests to find a good driver for FirePro V8800 on 
> windows 7 64bit HVM.
> I have been focused on ‘advanced features’: quad buffer and active 
> stereoscopy, synchronization …
> The results, for all FirePro drivers (of this year); I can’t get the 
> quad buffer/active stereoscopy feature.
> But they work on a native installation.
Can you describe the setup a little more?
How many graphic cards per guest?
How many guests? On how many hosts?
> The only driver that allows this feature is a Radeon HD driver 
> (Catalyst 12.10 WHQL).
> But this driver becomes unstable when an application using active 
> stereo and synchronization is closed:
> -The synchronization between two computers is lost.
>
> -The CCC can crash when the synchronization is made again.
>
> Someone have any clues about this?
I don't know exactly how this works on AMD/ATI graphics cards, but I 
have worked with synchronisation on other graphics cards about 7 years 
ago, so I have some idea of how you solve the various problems.
What I don't quite understand is why it would be different between a 
virtual environment and the bare-metal ("native") install. My immediate 
guess is that there is a timing difference, for one of two reasons:
1. IOMMU is adding extra delays to the graphics card reading system memory.
2. Interrupt delays due to hypervisor.
3. Dom0 or other guest domains "stealing" CPU from the guest.
I don't think those are easy to work around (as they all have to 
"happen" in a virtual system), but I also don't REALLY understand why 
this should cause problems in the first place, as there isn't any 
guarantee as to the timings of either memory reads, interrupt 
latency/responsiveness or CPU availability in Windows, so the same 
problem would appear in native systems as well, given "the right" 
circumstances.
What exactly is the crash in CCC?

(CCC stands for "Catalyst Control Center" - which I think is a Windows 
"service" to handle certain requests from the driver that can't be done 
in kernel mode [or shouldn't be done in the driver in general]).
--
Mats
> Thanks,
>
> Aurelien
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