Re: VGA passthrough and AMD drivers

[Mats Petersson <mats.petersson@citrix.com>]

On 07/12/12 16:51, 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?
>
> I’ve got 2 HP Z800 workstation with FirePro V8800, one per computer.
>
> It’s a setup used in CAVE system, I try (and its works, minus some 
> issues) to virtualize ‘virtual reality contexts’ that needs full 
> graphics card features.
>
> Intel Xeon E5640 CPU with Intel 5520 chipset
>
> cores_per_socket : 4
>
> threads_per_core : 2
>
> cpu_mhz : 2660
>
> total_memory : 4079
>
> >How many graphic cards per guest?
>
> One card per guest.
>
> >How many guests? On how many hosts?
>
> One guest per computer.
>

And of course, I just thought of some other questions:
What version of Xen are you using?
What kernel are you using in Dom0?

And just to be clear, there is only Dom0 and one Windows 7 HVM guest on 
each machine?

> >>
>
> >> 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]).
>
> After the application is closed, I launch the Catalyst Control Center, 
> the synchronization state seems to be good. But there is no 
> synchronization.
>
> If I try to apply any modifications of synchronization (synchro server 
> or client), CCC freeze and I need to kill it manually.
>
> I can set the synchronization back after this.
>

This clearly sounds like a software issue in the CCC itself. I could be 
wrong, but that's what I think right now. It would be rather difficult 
to figure out what is going wrong without at least a repro environment.

Whilst I'm all for using Xen for everything, there are sometimes 
situations when "not using Xen" may actually be the right choice. Can 
you explain why running your guests in Xen is of benefit? [If you'd like 
to answer "none of your business", that's fine, but it may help to 
understand what the "business case" is for this].

--
Mats
>
> I will try next week with others computers.
>
> Thanks for the reply,
>
> Aurelien
>
> --
>
> Mats
>
> >
>
> > Thanks,
>
> >
>
> > Aurelien
>
> >
>