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

What are the circumstances in which your comment about "Xen - limited
to 3GB for RAM" applies?  Is it in the case in which one uses multiple
GPU cards?

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)
(6GB Win7 HVM with passthrough of ATI 68XX and multiple USB
None of these tutorials mention a 3GB limitation.

The only recent reference to a 3GB HVM issue during passthrough is here:
which appears to link the issue with use of nvidia patches from here:
>From what I gather, nvidia cards perform a bit of undocumented voodoo
(by design) that has not been fully accounted for.

it sounds like there was a PV domain issue arising from e820 for which
a reliable workaround was incorporated into the mainline code some
time ago.

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

- Eric

>> Patrick,
>> 1) Xen's vocabulary
>> dom0 = the main (first) hypervisor, hosting all virtual machines -- like 
>> your Mac OS X
>> domU = any virtual machine.
>> This is not the real meaning but here I try to stay "understandable". But 
>> for better understanding please refer to http://en.wikipedia.org/wiki/Xen
>> My understanding is that your dom0 has to be replaced by Linux so you can 
>> run Xen. But for this part I am not a Mac OS X expert.
>> 2) More info  - details listed beow are only available for a Xen dom0 
>> running on Linux.
>> [Extracted]:....I've ended my testing with ESXi, because I was not able to 
>> passthrough sound device, and USB....
>> [Comment]: With Xen you can :)
>> [Extracted]: ...with stock ATI Radeon..;
>> [Comment]...Xen offers VGA PassThrough feature for ATI Radeon.
>> Here is a link to a Youtube video to run Crysis 3 on a domU Windows 7 64 
>> Bits with HD 7970
>> http://www.youtube.com/watch?v=GTnchEG4YtI&feature=player_embedded
>> As you can see
>> - I can use PCI Passthrough to add a XBOX 360 Paddle while playing Crysis 3 
>> (see at 09:12 in the Video)
>> - I have sound too :)
>> But it works on Linux domU too. Here is another Youtube video link
>> http://www.youtube.com/watch?feature=player_embedded&v=KzqOIMaBgX0
>> But you need to apply a few patches to able this feature with Xen 4.2 and 
>> over. Not very complicated to do.
>> Here are my instructions to do it but I know that there are currently better 
>> way to test it
>> http://www.davidgis.fr/blog/index.php?2013/03/13/935-xen-43-vga-passthrough-ati-card-hd-7970-changeset-26706
>> [Extracted]...memory allocation
>> [Comment]...Xen - limited to 3GB for RAM. A few developers are working on 
>> overpassing this limitation.
>> [Extracted]...no snaphost possible
>> [Comment]...If you used Xen with LVM is then snahshotting is easier to 
>> manage ;)
>> [Extracted] no sleep
>> [Comment] works on Xen for both Linux and Windows. The main issue is that 
>> you can reboot a domU without restarting the dom0.
>> [Extracted] Is it possible to create a virtualized desktop with VGA and PCI 
>> passthrough for 2 or 3 VM's running simultaneously (ie. each one with its 
>> own video card)?
>> [Comment] Yes it is doable. Never tested but from experience share with 
>> other Xen users  I know that it should be run fine.
>> Hope it helps.
>> Kind regards.
>> David.

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