Re: [Xen-users] PCI/VGA passthrough: differences between Xen and ESXi?

[Patrick Proniewski <patpro@xxxxxxxxxx>]

On 03 avr. 2013, at 01:26, Eric Shelton wrote:

> There are a number of HVM tutorial examples with well over 3GB:
> http://wiki.xen.org/wiki/Secondary_GPU_Passthrough (6GB Win7 HVM with
> passthrough of ATI 6970 and USB controller)
> http://wiki.xen.org/wiki/Comprehensive_Xen_Debian_Wheezy_PCI_Passthrough_Tutorial
> (6GB Win7 HVM with passthrough of ATI 68XX and multiple USB
> controllers)
> None of these tutorials mention a 3GB limitation.

That's great. Thank you for the pointers.
I've been into some trouble supporting a >2GB config with GPU passthrough on 
ESXi, but I've been able to work around with 2 lines of configuration. That's 
not exactly a surprise for me that GPU passthrough can be quite sensitive to 
the amount of RAM...


> Patrick:
> From the above examples, it seems like >3GB may be fine if you use
> ATI/AMD GPUs.  I have had fairly good experiences with passthrough of
> a single AMD 6570 with the patch mentioned here: 
> http://lists.xen.org/archives/html/xen-users/2013-02/msg00410.html
> although I did not explore how much or how little memory I could
> assign to it.  Note, however, that patch may make certain assumptions,
> such as that only one GPU is being passed through.  I'm not sure there
> is any unpatched release version (for example, 4.2.1) that reliably
> does GPU passthrough (PCI passthrough of less wonky devices has worked
> for some time).
> 
> I think the proposed multi-GPU setup may be putting you out on the
> bleeding edge (on the other hand, it sounds like it is absolutely no
> available under ESXi).  It's probably not impossible.  Maybe someone
> has already done it.

I'm not interested in passing through more than 1 graphics card per VM, and the 
best solution for me would be to pass through 1 graphics card to few VMs (I 
don't want to suffer from the noise, the heat, the cost, the power consumption 
of an array of graphics cards).
Technically, ESXi allows you to passthrough only 1 graphics card per VM, but I 
find no evidence that it won't allow passing through N graphics cards to N VMs.
Of course, low powered fanless graphics cards do exit, and I mould probably be 
pretty happy with them. Problem is, they use huge coolers, and you can't put 
many of them into a single enclosure.


>  However, how interested and/or comfortable are
> you with code & configuration tweaking, debug, and experimentation?

I'm highly competent in various IT fields, including system administration on 
FreeBSD/Unix. But the more I'm getting old, the less I want to spend my nights 
debugging config and playing with patches :)
Ten years ago I'd have setup a test box and played with Xen to achieve my 
goals. Now I'm more into finding a mature (or at least less experimental) 
solution.
My project is not urgent, I can wait one or two years without any problem. My 
Mac Pro has still few years of 24/24 operation before needing replacement. When 
this time will come, I'll consider a good hardware platform for home 
virtualisation (Supermicro's whisper-quiet workstation is my current choice).
I'll keep an eye on Xen, and may be give it a fast try in the next months, but 
probably not something as complete as my attempts with ESXi. More importantly, 
Xen would require I switch from the macintosh world to the hackintosh world. 

Thanks again for your replies, it helps me figuring out the state of GPU 
passthrough on Xen.

Patrick
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