PCIe Pass-through lanes and lane performance
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So I ordered some mini DP dummy plugs and took a look at this further today.
First thought...Just load Windows on the bare metal and see what the card does.
No problem. Loaded Win10, loaded the latest drivers, PCIe Gen4x8 lanes. Sweet. At least that works.
Put the XCP-ng drive back in, booted up, passed-through the GPU to a Win11 guest, updated the drivers, PCIe Gen1x1.
As I explained briefly in https://xcp-ng.org/forum/post/106479, this is mostly display as the real hardware may be running at a different speed.
Ultimately I need to install a Linux distro with a really current kernel on the bare metal and see how it sees the GPU. That might be a good project for tomorrow.
I think this just comes down to a combination of too new, not well supported hardware with some quirks and somewhat dated code and support in XCP-ng (ReBAR support in guests for example).
I did quick checks and I believe that ReBAR works; at least with UEFI guests (our OVMF build does support resizable bar), and it actually works as suggest https://xcp-ng.org/forum/post/106489 (VRAM BAR is 16 GB); but I didn't do extensive testing in that area.
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