Re: [Xen-users] VGA passthrough with Xen 4.3 and xl toolstack - performance degradation resolved?

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 03/13/2014 08:33 PM, H. Sieger wrote:
> I spent the last 8 hours testing VGA passthrough with a AMD Radeon 7770
> card. Here the setup:
>
> Hardware: Asus Sabertooth X79 with latest BIOS and VT-d enabled; i7
> 3930K CPU; Sapphire Radeon 6450 for dom0, Sapphire Radeon 7770 for domU.
>
> 1st trial - Linux Mint 16 64 bit with kernel 3.11.0-18 and Xen 4.3.0;
> Windows 7 Pro 64 bit; both installed on external USB3 disk:
>
> In short, a disaster. I first tried the xl toolstack I was using with my
> regular configuration (same m/b and CPU, but AMD Radeon 7770 for dom0
> and Nvidia Quadro 2000 for domU).
> I tried to make a new Windows installation in domU. After each shutdown
> of the domU I had to reboot the whole machine, else I would get libxl...
> errors and nothing. dom0 wouldn't even shut down, had to hard reset. I
> somehow managed to install Windows, but once I tried to install the
> graphics driver for the AMD card Windows sooner or later gave me a blue
> screen.
Did you build from source or use distro packages? If you are using the 
distro packages it is possible your distribution's packages are broken 
or old enough to contain regressions.
> Next I tried with xm. I started from scratch, setting up a new Windows
> LVM volume. xm create ... failed with "error 22". That sounds familiar.
> I had the same issue with my regular Nvidia setup some time ago with Xen
> 4.1.3. But I thought that by Xen 4.3 this was fixed?!
I'm sure I remember this bug and it was due to a regression at some 
point. Ah, here it is:
http://xen.crc.id.au/bugs/view.php?id=5

Regression introduced in XSA-46.

> In the bug report someone suggests to pass through only the first
> function of the graphics card, in my case PCI ID 02:00.0, and not
> specify the second (HDMI audio) function 02:00.1. I tried but no luck.
> Just to make sure, removed the graphics card from the PCI passthrough
> devices and only left a USB controller to pass through, which worked!
>
> Summary: Xen 4.3.0 still has some of the old bugs that I that had gone
> long ago. Or is that a kernel issue?
Where do your packages/binaries come from?

> 2nd trial - Linux Mint 13 64 bit with kernel 3.2 and Xen 4.1.2; Windows
> 7 Pro 64 bit; both installed on external USB3 disk:
I vaguely recall issues with a number of kernels. I'm currently running 
with 3.9.9 (I should have upgrade to 3.12 by now but 3.9.9 works without 
any issues for me so I am finding it hard to persuade myself to try 
upgrading.)
> I installed the long term release Linux Mint 13 that worked well when I
> started out with Xen VGA passthrough. After installation and upgrading
> all packages and the kernel, I installed Xen and then downgraded using
> "Force version" in Synaptic to the earliest Xen release available in the
> repos, which was 4.1.2 if I remember correctly.
> This time I only used xm. Installation went smooth, no hickups no
> nothing after multiple reboots of Windows. Passthrough works just fine
> with the AMD Radeon 7770. I ran the WEI, both prior and after installing
> the GPLPV drivers in Windows - it made no difference - 5.9 lowest score
> for disk (a 2.5" HDD attached via USB3), 2D and 3D graphics are 7.5,
> memory 7.9 (with 8GB for Windows), and CPU 7.8 (I gave it 8 of 12
> VCPUS). I even installed the Unigine demo and benchmark - it ran fine
> though the 7770 is really not up for it with 21fps.
>
> Summary: Xen 4.1.2 with an old 3.2 kernel works perfect with xm and VGA
> passthrough.
Does it continue working across domU reboots?

> To me this looks like some ancient bugs are still not fixed (with regard
> to xm), and probably never will since it's been deprecated. The sad
> story, however, is that xl has its own serious problems with VGA
> passthrough.
It works for me (Xen 4.3.0 with xl, kernel 3.9.9).

> Whatever it is, it's not an AMD driver issue. The problems start long
> before I even managed to install the AMD driver.
And with 4.1.2 you can reboot the domU multiple times without it 
resulting in massive slow-down, BSODs, or the card not coming up?
> Hope someone from Xen development has a look at this. Although this
> means reconfiguring my hardware, I'd be happy to help in debugging if
> anyone is willing to try and fix it.
Gordan


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