Xen project Mailing List

Hi Patrick,

I don't mean to jump in after you already got the information you wanted, but I thought I would throw in my two cents in hopes that it helps save you some time & effort.

> 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...

I wrote that second guide, it's a bit out of date so if you choose to use it know that things are a little different. ÂI have been using AMD passthrough on Windows 7 and Windows 8 since September, but I have yet to get it working in Linux, but I blame my own inexperience for that. ÂThere are links on my guide to youtube video walkthrough & very short HVM performance demo. ÂJust following the instructions will have you up and running in about 2 hours, but actually understanding how it all works may take quite a bit longer.

> Patrick:
> From the above examples, it seems like >3GB may be fine if you use
> ATI/AMD GPUs. ÂI 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. ÂNote, however, that patch may make certain assumptions,
> such as that only one GPU is being passed through. ÂI'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). ÂIt's probably not impossible. ÂMaybe 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.

I have shared the same card by shutting down one instance and booting another, but there is a performance degradation problem which I would say is due to the lack of FLR in consumer graphics cards. ÂThere are work-arounds but they will feel "hacky", just be ready to deal with major pains getting multiple machines using the same card and make plenty of backups. ÂI don't know how ESXi handles this problem, but if you do I would love to know more.

> ÂHowever, 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.

I use a macbook so I know where you are coming from, I totally prefer the mac/unix environment for a workstation. ÂUnfortunately I am pretty sure that OS X requires a UEFI bootloader, and that only exists in upstream-qemu which to my knowledge does not yet work with VGA Passthrough. ÂYou would be stuck in SDL or VNC, or maybe ssh, not that those are necessarily bad.Â

Good luck with your adventures,

~Casey

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