powerhouse wrote:1. Single card VGA passthrough: IIRC, in order to make do with one GPU, you would need to compile pciback into the kernel and add the pciback option to the grub file. The idea is to bind the graphics card to pciback before the graphics driver (dom0) gets loaded. But don't take my word on that, it's been a while since I played with it. See also http://www.overclock.net/t/1205216/guide-create-a-gaming-virtual-machine for a great tutorial based on Fedora 16. It's a very long thread with tons of useful information.
In order to release a passed through PCI device, use:
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virsh nodedev-reattach pci_0000_0a_00_0
This reattaches the PCI device to dom0. It works well with USB controllers, but I haven't tested my graphics card yet. I have some doubts about reassigning graphics cards to different domUs, or back to dom0.
While I was considering compiling my own kernel once I had verified this works with my hardware (still waiting on shipments) I'd just assume not rock the boat too much with VGA passthrough. On the KVM side of the pond you have lockups and performance degradation being reported. I'll be happy enough to get it to work and I've already ordered my second video card. It's an interesting concept though. I like messing around with new stuff but generally with the eye on making it stable enough for everyday use.
2. AMD CPUs: You wrote a lot about AMD CPUs. I'm afraid I haven't got a clue about AMD CPUs, the last time I used one was some 7-8 years ago. A few years ago Intel integrated the memory controller into the CPU - I believe AMD uses another chip to host the memory controller, so it would also depend on the motherboard.
For both AMD and Intel, all parts must support IOMMU: CPU, motherboard (chipset), and BIOS, though in some cases the CPU doesn't play part in IOMMU (Intel Core 2 Duo, for example). What I mean is that you need to make sure that the combination of all three supports IOMMU.
lol That's funny I was just thinking to myself that I haven't messed around with desktop Intel processors since the days of the venerable 440BX chipset and Pentium II/III (released in 98). I'm probably one of the few people that bothered building a dual processor celeron machine that served faithfully for over a decade 24/7 (somebody really wanted a dual processor server but didn't want to pay for it lol) I did have some Xeon servers that I built and maintained a few years back so I'm not totally out of the loop. But on the desktop I haven't built a intel machine for about 15 years. I wouldn't call myself an AMD fanboi even if the first PC I built myself was a 386DX-40Mhz. Maybe I just have a soft spot for the underdog, but I can't deny that Intel has the performance lead more often than not.
As far as the memory controller goes it was actually AMD that first incorporated it with the Althon 64 in the early 2000's. For a short while that was one of the technical disadvantages that Intel had. The front side bus had to deal with memory requests as well as the I/O. To compound that problem the bandwidth available could hardly deal with the increasing data transfer rates of memory. Hypertransport also allowed for point to point links between processors which previously was handled by the FSB. The Althon 64 really was a design win for AMD that they didn't/weren't able to capitalize in the long run. Intel has certainly caught up and surpassed AMD since then.
I'll probably spend some time refreshing my memory on Intel tech today as I might upgrade my home server with it rather than continue to give it my AMD hand-me-downs.
Oh, if you referring to my speculation of using those APU's for VGA passthrough it was just a thought experiment. I do know you have to have support across the cpu/bios/MB and on paper they do. At least as far as the MB manual's bios settings indicate. IOMMU is a feature that is hard to get definitive info about from manufacturers. Until someone actually tries it you can't say for sure. In my searching for someone who has I noticed you've fielded a question about APU's over on phronix (man you have threads everywhere ) but it doesn't look like the guy has reported back on any success or failure. Though what he was describing was a bit different than what I had in mind. He wanted to passthrough his only GPU (from the CPU) to his DomU. I was talking about using the integrated GPU as a cheap option for the Dom0 in a dual card setup. The integrated GPU in AMD's processors are considerably better than their Intel counterparts so I can see it's application in a HTPC build. I think the problem with his idea is that is rather inconvenient and isn't computing in the living room supposed to be focused on ease of use? I wouldn't want to have to fiddle with things when I just want to kick back and relax.
As far as my VGA passthrough build goes I'm playing it safe and testing things as I go. My sister has a newer IPS monitor that fits the bill for my use of the HDMI audio use so I'll probably test the audio on hers before I buy my own. She's never used the audio jack and it'd be just my luck that the implementation is shoddy. I'll probably throw my second video card into my HTPC that's running Mint 14 to test for any driver issues. Well you get the idea.
One question did just come to mind though. The last time I tried messing with windows in a VM I was using XP and I've upgraded to Win 7 since then. Does Win7 give you a grace period on activation like XP did? I was just thinking it might be prudent to experiment with Xen on a separate drive. I've had my fill of resizing and moving partitions around on my last build. I'd like to confirm it works before I go toasting my dual boot. I really hope vga passthrough works for me as I really like the idea of switching to GPT and LVM completely. Though yesterday I started toying with the idea of trying the linux implementation of ZFS in conjunction with XEN but the suggested memory requirements and the added complexity has sufficiently deterred me. Maybe down the road when I upgrade my memory and I've ironed out Xen and VGA passthrough. Doing both at once sounds headache inducing.
Though my old habits from my days doing IT work might overcome reason... Raid... everywhere....