[X570 Gaming ITX] GPU error with PCIe bifurcation

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   I've just built a new computer, my first using PCIe Bifurcation. I wanted a small PC with 25 Gigabit Ethernet and a GPU, each of which is usable with PCIe Gen3 x8. The problem is that Windows 10 (and Ubuntu 19.10) don't use the GPU when it is in the second x8 slot of the riser.

Motherboard: Asrock X570 Gaming ITX/TB3 (BIOS 1.90)
CPU: Ryzen 3700X
Memory: Corsair Vengeance LPX DDR4-3200
Video Card: Zotac GTX 1070
Network Card: Mellanox ConnectX-4 Lx Dual 25 GigE
Riser: Ameri-Rack ARC1-PELY423

I've tested four configurations, three of which work.

1) PCIe slot set to x16  --> GPU works directly in the motherboard slot, runs at x16 rates
2) PCIe slot set to x16  --> GPU works in either riser slot, runs at x8 rates
3) PCIe slot set to x8x8 --> GPU works in first riser slot, runs at x8 rates
4) PCIe slot set to x8x8 --> GPU does not work in second riser slot

I need to get the GPU working in the second slot because the riser slots are next to each other so a 2 slot wide GPU in the first slot blocks the second riser slot.

The GPU does always work to display the BIOS. I don't know how the GPU driver use changes between the BIOS and an operating system. I'm going to try using Remote Desktop to access Windows after it boots to see if I can get more information.

Does anyone have any advice on how to debug this? Has a GPU in a second slot been tested by Asrock or anyone else?

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Forvak Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 03 Dec 2019 Status: Offline Points: 6	Post Options Post Reply Quote Forvak Report Post Thanks(0) Quote Reply Topic: [X570 Gaming ITX] GPU error with PCIe bifurcation Posted: 03 Dec 2019 at 6:22pm
	I've just built a new computer, my first using PCIe Bifurcation. I wanted a small PC with 25 Gigabit Ethernet and a GPU, each of which is usable with PCIe Gen3 x8. The problem is that Windows 10 (and Ubuntu 19.10) don't use the GPU when it is in the second x8 slot of the riser. Motherboard: Asrock X570 Gaming ITX/TB3 (BIOS 1.90) CPU: Ryzen 3700X Memory: Corsair Vengeance LPX DDR4-3200 Video Card: Zotac GTX 1070 Network Card: Mellanox ConnectX-4 Lx Dual 25 GigE Riser: Ameri-Rack ARC1-PELY423 I've tested four configurations, three of which work. 1) PCIe slot set to x16 --> GPU works directly in the motherboard slot, runs at x16 rates 2) PCIe slot set to x16 --> GPU works in either riser slot, runs at x8 rates 3) PCIe slot set to x8x8 --> GPU works in first riser slot, runs at x8 rates 4) PCIe slot set to x8x8 --> GPU does not work in second riser slot I need to get the GPU working in the second slot because the riser slots are next to each other so a 2 slot wide GPU in the first slot blocks the second riser slot. The GPU does always work to display the BIOS. I don't know how the GPU driver use changes between the BIOS and an operating system. I'm going to try using Remote Desktop to access Windows after it boots to see if I can get more information. Does anyone have any advice on how to debug this? Has a GPU in a second slot been tested by Asrock or anyone else?

rumle23 Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 21 Dec 2019 Status: Offline Points: 1	Post Options Post Reply Quote rumle23 Report Post Thanks(0) Quote Reply Posted: 21 Dec 2019 at 8:16am
	Hi I am almost in the same boat as you. The only difference is that I am on the 3900X and trying to connect 2 GPU's in the riser. When having both connected and PCIe slot set to x16, the graphics card in the second slot works. When set to x8x8 none of the GPU's work. I have tried booting into linux and ssh into it from another pc. Both GPU's appears to be present when listing connected devices, but looking through the xorg log it seems that the GPU's cannot be initialized. It also appears that the link speed is only 2.5 GT/s and is PCIe gen 3 x8 not supposed to be 4 GT/s? What BIOS settings have you tweaked? I am not able to display BIOS either and I find it interesting that you can display BIOS.

Forvak Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 03 Dec 2019 Status: Offline Points: 6	Post Options Post Reply Quote Forvak Report Post Thanks(0) Quote Reply Posted: 24 Dec 2019 at 10:23am
	I've been able to work around this issue. It turns out that (I don't know why) the PCIe Bifurcation doesn't work for me if there is no card in the first PCIe riser slot. When I put in my NIC card in slot one and enabled x8x8 both cards started working. I guess this doesn't help you rumle. The only setting I'm changing is the x16 to x8x8. Separately I have an issue of the BIOS settings resetting from time to time. I think this is to do with the RAM XMP profile, but need to figure out how to debug this.