PCI-E Bifurcation

groupmsl

Minimal Tinkerer
Nov 8, 2017
3
3
Hello,

I've just managed to get hold of an Ameri-Rack PCIe bifurcation riser which I am excited about! It should work with an ASRock’s AB350 Gaming-ITX and also a Supermicro ITX board that I have. I have a question about enabling bifurcation though.

Neither of my boards have onboard graphics, so I need a GPU in a PCIe slot to configure bifurcation. What order have others done the process of adding the bifurcation riser? Do you enable x8x8 in the BIOS first, then add the bifurcation riser, or the opposite: add the bifurcation riser and then configure the BIOS for x8x8?

Not knowing enough about the PCIe bus and pinout I'm concerned that doing this process in the wrong order could cause damage to the motherboard or PCIe cards.

Thank you
 
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Biowarejak

Maker of Awesome | User 1615
Platinum Supporter
Mar 6, 2017
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Hello,

I've just managed to get hold of an Ameri-Rack PCIe bifurcation riser which I am excited about! It should work with an ASRock’s AB350 Gaming-ITX and also a Supermicro ITX board that I have. I have a question about enabling bifurcation though.

Neither of my boards have onboard graphics, so I need a GPU in a PCIe slot to configure bifurcation. What order have others done the process of adding the bifurcation riser? Do you enable x8x8 in the BIOS first, then add the bifurcation riser, or the opposite: add the bifurcation riser and then configure the BIOS for x8x8?

Not knowing enough about the PCIe bus and pinout I'm concerned that doing this process in the wrong order could cause damage to the motherboard or PCIe cards.

Thank you
Should be fine doing the change while it's plugged in, AFAIK. It's basically just a dumb riser until the setting is enabled. But you can always play it safe and just put your GPU in like normal to change the setting.
 
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rokabeka

network packet manipulator
Jul 9, 2016
248
268
yes, he will be fine doing it with the videocard inserted.
I will fire up a tiny build log soon, where I used the very same board with a nvidia gt710 and the amerirack riser. the videocard is a x8 anyway, but I think in case of using a x16 gpu the only thing will change at the next reboot is that e.g. gpu-z (if you are on windows) shows you x8 instead of the x16.
 

groupmsl

Minimal Tinkerer
Nov 8, 2017
3
3
Thanks guys. I've had time to try this with the ASRock AB350 Gaming-ITX board this morning, I inserted the riser first (with only my GPU installed) and then changed the relevant setting (x8x8) in the BIOS.

After that I installed an HDMI capture card (BlackMagic Intensity Pro 4K) in the other slot in the riser. My PC seems just as stable as normal and detects both cards without issue.

The only thing I have noticed is that my GPU is running at x2 speeds. If go back to x16 in the BIOS (and take out the HDMI capture card) the card runs at x16, unsurprisingly, but when I enable x8x8 the card actually runs at x2. I assume that's just what my GPU drops down to if the full 16 lanes aren't available?
 
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Biowarejak

Maker of Awesome | User 1615
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Mar 6, 2017
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Thanks guys. I've had time to try this with the ASRock AB350 Gaming-ITX board this morning, I inserted the riser first (with only my GPU installed) and then changed the relevant setting (x8x8) in the BIOS.

After that I installed an HDMI capture card (BlackMagic Intensity Pro 4K) in the other slot in the riser. My PC seems just as stable as normal and detects both cards without issue.

The only thing I have noticed is that my GPU is running at x2 speeds. If go back to x16 in the BIOS (and take out the HDMI capture card) the card runs at x16, unsurprisingly, but when I enable x8x8 the card actually runs at x2. I assume that's just what my GPU drops down to if the full 16 lanes aren't available?
It should be negotiating to x8. Have you tried swapping their positions? And have you tried verifying the connection with the tool in GPU-Z? Some power saving features can drop your bandwidth when not using a 3D application.
 
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groupmsl

Minimal Tinkerer
Nov 8, 2017
3
3
It should be negotiating to x8. Have you tried swapping their positions? And have you tried verifying the connection with the tool in GPU-Z? Some power saving features can drop your bandwidth when not using a 3D application.
I tried this last night (been away for work which is why it took so long). I used GPU-Z and it says the GPU is capable of PCIe 3.0 x16, and when idle it's running at PCIe 1.1 x2. When I run the tool to stress the GPU the connection only changes to PCIe 3.0 x2, so sounds like something is wrong. I wonder if it's something to do with my motherboard - has anyone else tried with the ASRock’s AB350 Gaming-ITX?

At some point I will try with my Supermicro board and see if I get any different results.
 
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Biowarejak

Maker of Awesome | User 1615
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Mar 6, 2017
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Might be worth putting it in performance mode in your vendor's display settings. Might also be an issue with the cable or a lack of lanes on the CPU. Could also double check the bifurcation split in the bios. Tbh though, your GPU might not need all 8 lanes, so I'm not sure :p
 

rokabeka

network packet manipulator
Jul 9, 2016
248
268
maybe there is something with regarding the pcie versions (v3.0 vs v2.0). I have pretty much the same here, with having a pcie v3.0 x8 nic and the nv gt710 x8 v2.0. the gpu runs only at x2.

according to blackmagic that card anyway is a x4, but could not figure out which version.
unless the negotiated bandwidth is too low (e.g. dropping frames), I would not worry.
 
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davidm71

Minimal Tinkerer
Dec 17, 2017
3
3
Hi Guys,

Ready to bifurcate my last pci-e slot on my X99 board. Read that it should be supported according to Intel data sheets for the 6850k but there has been debate wether you need the manufacturer to provide hardware support nevermind software support. Thing is on my X99 the last 4X lanes go to waste when the pcie #5 8X slot share bandwidth with the M.2 slot if both occupied. However with a dual riser perhaps I could get my device on the other pcie slot 2nd half and not step on the M.2 lanes.

So I looked in Ami BcpEdit tool and found options under IntelRCSetup and IIO 0-4 to set the IOU2 ports to 4x4 bifurcated mode. Wonder if this might work or not. Need to order a dual riser card and cable to test this out.,

Thanks
 

jtd871

SFF Guru
Jun 22, 2015
1,166
851
Hi Guys,

Ready to bifurcate my last pci-e slot on my X99 board. Read that it should be supported according to Intel data sheets for the 6850k but there has been debate wether you need the manufacturer to provide hardware support nevermind software support. Thing is on my X99 the last 4X lanes go to waste when the pcie #5 8X slot share bandwidth with the M.2 slot if both occupied. However with a dual riser perhaps I could get my device on the other pcie slot 2nd half and not step on the M.2 lanes.

So I looked in Ami BcpEdit tool and found options under IntelRCSetup and IIO 0-4 to set the IOU2 ports to 4x4 bifurcated mode. Wonder if this might work or not. Need to order a dual riser card and cable to test this out.,

Thanks

Let us know which motherboard you're using and how it goes.
 
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davidm71

Minimal Tinkerer
Dec 17, 2017
3
3
Let us know which motherboard you're using and how it goes.

Hi all,

Just wanted to keep in touch and let you guys know about my efforts. Basically I was able to successfully mod the bios of a MSI Godlike X99A to bifurcate the last 8X PCI-E Slot. I altered the bios menu to create a new entry entitled 'PCIE Bifurcation Mode'. I used a Supermicro RSC-R2UU-2E4R 8X to 4X4X card to assist in using the posterior last 4 lanes of the PCIE#5 slot and at the same time keep my onboard M.2 Samsung 950 Pro running at 4X through the Cpu while I have a Plextor M8Pey AIC Card hooked up to the riser card. Only issue I am having is sometimes it will reboot at 2.5 GT/S speed on the Plextor drive with 4X lanes wether or not its hooked up directly to the riser card or not such that it goes away back to 8.0 GT/S with bifurcation turn off in bios.

The only solution I have found to bring it back to 8.0 GT/S mode is to reboot cold from being powered off completely, or reinstall the NVME drivers and reboot. Think this has something to do with the latency L0 + L1 values but not an expert on those details. I have been experimenting with using SETPCI windows port tool to set certain registers in the IO controller to reset the link speed unfortunately I can only up it to 5 GT/S from 2.5 on the fly, or bring it down to 2.5 or 5.0 from 8 GT/S via software command. When I set the link speed back to 8.0 GT/S unless it was already at 8.0 it doesn't come back up. I think however performing a reboot after using SETPCI brings it back to 8.0. If this is true then I could create a batch file to run at every startup so it never degrades.

Any bios engineers out there?! Lol...

Thanks.
 

NADRIGOL

Caliper Novice
Sep 25, 2017
23
23
Yes, as rock z370 itx works with bifurcation :)

Any more details from your experience. Just learning about bifurcation and considering it for my next build. Wondering what riser you paired with the asrock and if everything went smoothly?

Have there been successes running two Nvidia cards in SLI over bifurcation?
 
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