PCIe Pass-through lanes and lane performance

TeddyAstie

FYI I will get my hands on a Intel Arc Pro B50 to make various tests with it (in the next weeks). If something don't behave as expected, I will try to find a solution.

JamesG

@TeddyAstie I think there's alot of interest in the Intel platform because of the lack of ridiculous licensing for virtualization features. The problem is that you need a pretty current 6.x kernel to use them and XCP-ng/XenServer is just stuck on a really aging kernel right now.

As exposed in this thread, the PCIe pass-through isn't really working properly under XCP-ng.

Even if pass-through worked, that's kinda lame because the real purpose would be to chop up the GPU into SR-IOV instances so multiple workloads could have a GPU.

The Proxmox community is already rockin' and rollin' with this. I watched a video a couple of days ago where a B70 was chopped up into Qty.4, 8GB GPU's via SR-IOV and passed to clients.

No ridiculous mega-$$$$ licensing. It just worked.

JamesG

@TeddyAstie

Thought...If you want access to a server with a B50, I think I could setup VPN access and put a host online with IPMI access for you to do whatever you want with.

You will have an AMD Epyc 7302 with 64GB of ram some flash and HDD storage, and an Intel B50. PM me and we can work out the details of what you need to experiment with, and I can setup some remote access for you to get into the system.

I will gladly work with you guys any which way I can to move this forward.

TeddyAstie

@JamesG Don't bother, I'm in PTO next week; so I may get access to hardware when I'm back.

pandusen

@andriy.sultanov

@andriy.sultanov said:

@pandusen As Teddy said above, you can't passthrough a PCI bridge, so there's no PCI devices xapi shouldn't omit here.

I am not trying to pass through the bridge only the end points. The Intel arc's have 2 end points: The GPU and the Sound device. "xe pci-list" only reveals the GPU, not the sound device. (this works for nvidia and AMD)

But "going the xen-cmdline way" shouldn't break anything, that's what xe pci-disable-dom0-access does behind the scenes. What issues did you see? Which steps did you follow?

the sound device is available in the lspci list and can be passed through using CLI.
But doing so, (using CLI for passtrough) undoes everything done using xe or the passthrough gui in XO. and results in this:
https://xcp-ng.org/forum/topic/10609/xcp-ng-8.3-pci-passthrough-issue
so yes, its does break something.

dkidd255

@jamesg @teddyastie, any further findings on this?

I am building an AI Inference server with a handful of Arc Pro B70's and a Supermicro H12SSL-i MOBO + 128GB of ram. I was hoping to use xcpng as a hypervisor to setup different VMs / software setups, but have also run into roadblocks with pci passthrough.

I'm somewhat of a novice on low level issues like this but if there is any info i can provide to help with the support of these GPUs for passthrough, happy to do so.

Going to give proxmox a try, then bare metal but just wanted to add another somewhat different use case behind the Battlemage cards.

JamesG

@dkidd255 I'm a LOOONG time XCP/XenServer/XCP-ng user in my homelab...And it pains me to say this...

But this just works in Proxmox.

If you want to help us dig in and troubleshoot/explore this topic...Fine.

If you want to actually use your hardware and make progress on your ideas, go to Proxmox.

I seem to recall some recent firmware shenanigans from Intel. Intel maybe thought a little too much of their hardware, or they've decided to just scale things back a bit, but newer versions of firmware have reduced VF's available. I don't think the B70 is impacted by this, but it has massive memory in comparison to the smaller cards.

TeddyAstie

@dkidd255 @jamesg
I didn't forgot about it, but I still don't have access to relevant hardware (for reasons outside of my control).

In the meantime, if that happens to be related, can you try the patch that allows disabling hvm-pirq (this is going to be globally available soon) ?

pandusen

@JamesG Yeah, its scary that GPU passthrough still has a low priority for XCP-ng, during the boom of AI and local LLM Inferencing. I my self am starting to plan a move to Proxmox, though I do not really wish to move, cause I like XCP way better and have been with them for a long time... But that is just comfort...In the end, everything it comes down to is the capability and performance of the running VM guests.

dkidd255

@JamesG, Yea i ended up having to go with a bare metal ubuntu install + docker containers for everything and have been off to the races, I would still like a hypervisor but unfortunately had to move on.

The software stack on these intel's gpus is still maturing but i'm running some pretty impressive models on them and for the money it has been a good investment, hopefully these will gain some popularity and get better support all around.

GPU hosting definitely deserves some attention from xcpng. I would buy some licenses for some production use cases but things like this and nested virtualization (completely unrelated but also something i ran into this past week) needs attention.