PCI-E Bifurcation

LukeD

Master of Cramming
Case Designer
Jun 29, 2016
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SLI finally working ?
Yep. Tomorrow ill do some performance tests as I need to hook up the GPU's to some water. I was running them dry :/



I've been working on a custom case for two bifurcated GPU for quite some time. Hope to achieve something around September.
Minimum I can achieve with liquid cooling (2U height) :
With AMD GPU's i don't think you'll have an issue. With nVidia though, using any hacks and designing a product around it is suicide really.
 

LukeD

Master of Cramming
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Jun 29, 2016
425
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Happy to say It works exactly as it should :)
No artefacts, no funny business :)

Mind you this was no apples to apples comparison as I only have 7700k benchmarks to compare against... and I can't be bothered to set this up on an ATX X370 board ... but the performance diff is consistent.



 

Phuncz

Lord of the Boards
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May 9, 2015
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No custom BIOS. I haven't heard back from Asrock, so I did a little custom BIOS tweaking myself :) Was easier than I expected to be honest :)
But is it legal then ? Because it seems you are circumventing Nvidia's SLI licensing. I personally am not a fan of this "pay for a sticker" type licenses but I'd hate to see Nvidia's Legal department rain down on you like a meteor shower.
 

LukeD

Master of Cramming
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Jun 29, 2016
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Honestly ... i think it would be edging in the grey areas :)
But ... proving something can work just goes to show that companies like Asrock and Gigabyte very well could support SLI over bifurcated PCIe. Just a matter of paying $10 to nVidia for the sticker :)

P.S. Maybe I can pay $10 to nVidia for the sticker :D
 

Biowarejak

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Mar 6, 2017
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But is it legal then ? Because it seems you are circumventing Nvidia's SLI licensing. I personally am not a fan of this "pay for a sticker" type licenses but I'd hate to see Nvidia's Legal department rain down on you like a meteor shower.
I don't think that bios hacking tends to be attacked by their legal department, you just can't say that SLI is officially supported or anything. It's a strange situation because you have to deal with both nVidia and the motherboard manufacturers
 
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rokabeka

network packet manipulator
Jul 9, 2016
198
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Gents,

by browsing the net it looks like Asrock has the AMD PBS menu option also on B350 boards and it had a config option to switch PCIe between x16 and 2x8 mode. But with the latest BIOS update they made it disappear. I have sent a question to Asrock tech support but no reply yet.

So the question is: despite of the official chipset feature list from AMD is it possible that e.g. Asrock Fatal1ty AB350 Gaming-ITX board also could support bifurcation? that is the only feature I need, I would not go with the x370 version if possible.
 

ChainedHope

Airflow Optimizer
Jun 5, 2016
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Gents,

by browsing the net it looks like Asrock has the AMD PBS menu option also on B350 boards and it had a config option to switch PCIe between x16 and 2x8 mode. But with the latest BIOS update they made it disappear. I have sent a question to Asrock tech support but no reply yet.

So the question is: despite of the official chipset feature list from AMD is it possible that e.g. Asrock Fatal1ty AB350 Gaming-ITX board also could support bifurcation? that is the only feature I need, I would not go with the x370 version if possible.
You might be able to do some custom BIOS work and get the feature back if it was fully developed on the board. While the specs say that only X370 and X300 support it, that doesnt mean you cant make it work if you know what your looking for. If you can get your hands on the older BIOS before they took it out and the newer one you can do a comparison on the files and find the areas that changed. It might just be that they took out the option and left the base code there. Worst case they never implemented it and just reused the BIOS from the X370 version which means you will most likely need to go with the X370 version. Making the implementation yourself would be more work than spending the extra money at that point.
 
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T_Tank

SFF Lingo Aficionado
Mar 16, 2017
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so while running duel gpu's over bifurcation sounds cool something came to mind. A 1 slot gpu like the galax katana then a strong sound card or pcie x16 based SSD or really any expansion card that can fill in the gap where the motherboard might had skipped out on something. Aren't there nvme to pcie adapters aswell?
 

rokabeka

network packet manipulator
Jul 9, 2016
198
228
You might be able to do some custom BIOS work and get the feature back if it was fully developed on the board.
[...]
Making the implementation yourself would be more work than spending the extra money at that point.
Yep, that's the idea. I just need the verification from an AB350 owner who tried it. If works, then playing with the BIOS is an option. If it have never actually worked before then I jump to x3xx immediately.
 
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LukeD

Master of Cramming
Case Designer
Jun 29, 2016
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Its also possible Asrock left the option there by accident but it was broken / not functioning from the get go.
 
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aquelito

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Feb 16, 2016
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@T_Tank I tried both times to run a non-PEG GPU (a 750 Ti and GTX 1050 Ti) with two different bifurcated risers and both times they wouldn't be recognized in WIndows 10.

Would be worth trying with a SSD or sound card for instance : I don't have both !
 
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Biowarejak

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@T_Tank I tried both times to run a non-PEG GPU (a 750 Ti and GTX 1050 Ti) with two different bifurcated risers and both times they wouldn't be recognized in WIndows 10.

Would be worth trying with a SSD or sound card for instance : I don't have both !
Did you use a powered riser?
 
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T_Tank

SFF Lingo Aficionado
Mar 16, 2017
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dont' have anything to do such a test but just a thought if it be viable?
 

aquelito

King of Cable Management
Piccolo PC
Feb 16, 2016
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Did you use a powered riser?
I try to avoid having a second riser daisy-chained to the bifurcated riser. So no, no powered riser.

However, C_Payne let the possibility on his custom riser to provide additional power. Not tested yet as the +12V line has not been cut on the riser and you might expect weird behaviours.
To quote his own words :

As for the GND and 12V, i intended those PAD's for additional power supply. I didnt try it yet though. They are directly connected to the 12V rail... So they could also supply additional power to the motherboard which could result in unexpected behaviour.
i did not try high Power GPU yet... It works unpowered with my Nano's.

@T_Tank I'll try with a M.2 Adapter or Wifi card and a GTX 1070 Katana... in September :)
 
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LukeD

Master of Cramming
Case Designer
Jun 29, 2016
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Well the Amerirack Bifurcated riser did have enough power for 2 x 1080ti's
The cable didn't get excessively hot.
 
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Aibohphobia

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Feb 22, 2015
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Couldn't that damage the motherboard in the long run since it's drawing more than 66W from the slot?
 

LukeD

Master of Cramming
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Jun 29, 2016
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I would have thought I'd feel the cable get warm if it was doing that. 1080ti can't exclusively draw power from the PCIe connectors if it doesn't get enough power from the motherboard does it ?
 
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