Is it possible to run a Crossfire setup when using a bare metal hypervisor like KVM or Xen?
The latest cards are using the third generation of crossfire called (XDMA) which opens a direct channel of communication between the cards. Is this just marketing slang or does it allow passed through cards to work in tandem?
Can't speak on behalf of all of your comments in confidence, but from what I understand doing PCI pass-through will allow you to utilize both cards as the communication is done from Windows to the cards directly; exactly the way you would have the cards running from a bare-metal OS.
Feel free to correct me if I'm wrong (as I type on the internet...).
As far as Windows and your video driver are concerned, the GPUs are indistinguishable from a non-passthrough GPU on a bare-metal OS. In theory, it should work fine, as long as you passthrough both GPUs, but I would guess that very few people have ever tried it, and you'd probably be on your own if you run into issues.
Just Google VFIO, dual cards wont be possible... I think, but PCI passthrough direktly to the VM. Its a very tricky process though. Good luck, you will probaly need it xD. For more info E-Mail me ( currently on phone ) [email protected]
With the HD7k+ cards and a recent kernel and recent kvm-qemu, it's possible to run XFire, but there are some tweaks you have to make to your guest Windows 7 (a guest Windows 8 doesn't work in my experience, but there are probably also fixes for that). This is amply documented on both Arch and Gentoo wikis and fora (and probably others also, since VGA/PCI passthrough to a Windows client has been VERY popular since about kernel 3.9).
However, it's best to use the HDMI audio, because for some reason, using emulated audio lags out even more when using crossfire than without. Whereas using emulated audio, games are still playable with the audio offset and overhead with one GPU card in PCI passthrough, even though the latency is noticeable, it becomes absurd when using two GPU cards in PCI passthrough. The easy solution is to use the GPU HDMI audio (which is better anyway for games because TruAudio, and which is also way more convenient when you switch inputs on your monitor between host and client, because you always get the sound that goes with the screen that you see instead of all audio, which can be confusing. I leave the host to the system audio, so that I always hear all notifications from KDE Connect and KMail for instance, but only use HDMI audio passed through from the monitor for the guest.)
Another thing that doesn't really work, is overclocking the GPU's in the client using the amdccc. You have to use amdcccle or the community fork for tweaking amd cards. I would advise not to overclock the cards at all when doing XFire in passthrough though, because it leads to regular BSOD's in the Windows guest when you boot the container up.
Thanks for the support so far. I'm in this weird situation where I don't have any old hardware to test on. At the same time I'm looking into buying new hardware which no one else has any experience with.
I'm probably just going to dive in when the Intel X99 boards and AMD R9 285 become available here.
Do you guys have any motherboard brand recommendations when it comes to Linux support? I'm already aware that I should go for an Intel network adapter. For audio I have a USB interface from Creative that should work according to h-node.
X99= high performance
R9 285 = medium performance (about the same as R9 280)
Doesn't fit together that well imo.
There is bound to be a high end Tonga card coming out in the foreseeable future, I would go for those on X99. If it's for compute, a FirePro might be an even better choice. If it's for game, better spend extra on GPU and less on CPU, because there is no gaming performance benefit at all in X99 (TechofTomorrow did a video with an fps comparison), it's even slower for some games than X79.
The R9 285 seems to make sense when playing at 1080p and hits an interesting price point. I would like the flexibility of having multiple cards to run in tandem or assign to separate VMs.
The X99 should give me some headroom to run multiple VMs in parallel for local development servers, a media server, Bittorrent and IRC client, etc.. It should be able to run my own cloud.
Yeah, X99 can do that. So can a Raspberry Pi though.
We should sticky and combine all the KVM threads