Does the UE4 engine support SLI?

Development Programming & Scripting
1

Does the UE4 engine and development tools support SLI? I am building a PC and i just need to know if its worth getting two GTX 760s

2

Hello,

Out of the box, if you wish to use all the features of UE4, you should forgo SLI.

The most common form of SLI is know as AFR (Alternate Frame Rendering) where each GPU handles a different frame. [ This is what we did with Samaritan on UE3 - 3 GPU’s each handling a different frame ].

The deferred rendering techniques used by UE4 rely on data from the previous frame to render the current frame and as a result are not SLI friendly. You could investigate which features are needed for SLI and potentially avoid them, however since that is not a usecase we have here at Epic, i’m not sure how well it will work as we keep extending UE4 with new functionality.

3

Hi there,

I am working on a VR project and was hoping to take advantage of NVIDIA VR SLI. The idea of having each GPU handle each eye is really interesting and seems to make the most sense for VR performance going forward. Is Epic planning to support this feature in the future or am I still better off getting one high powered card?

Thanks in advance!

4

While I am no dev for Epic, I bet that if you are interested in such a feature, it would be better to take in the two GPUs as it would allow you to test that feature better. For people consuming games, A single high powered is ALWAYS BETTER, but if you can make it work, that dual GPU idea would be fantastic and offer possibly better performance than that single GPU.

5

Hi, as per above and Crossfire support?! - Feedback & Requests - Epic Developer Community Forums it appears there are no plans for UE4 SLI support.

However for VR, apparently Nvidia GameWorks VR SLI is to be integrated into UE4 as per Nvidia announcement here: Gaming Archives | NVIDIA Blog

Here’s some slides on GameWorks VR in general: https://developer.nvidia.com/sites/default/files/akamai/gameworks/vr/GameWorks_VR_2015_Final_handouts.pdf

So that should enable VR SLI in UE4 when it comes out.

Of course, if someone from Epic can comment, that would be great.

6

Yeah Epic Games, please comment!

I am trying to work on gtx 970 sli, performance in editor is much better but after clicking “vr preview”, whole pc is going down… Is there anything I can do?

Cheers!

7

I am trying to work on gtx 970 sli,
performance in editor is much better
but after clicking “vr preview”, whole
pc is going down… Is there anything
I can do?

the_palion your computer was crashing probably because of quarrel between Oculus Drivers and UE, not because lack of support for SLI. Instal new Oculus SDK for Windows V1.3.0 and UE 4.11.1 and your computer will stop going down in VR Preview.

BTW anybody know is there any solution to turn on 2x GTX 900 series in SLI mode in UE??? I don’t believe this is impossible. I’m only graphic designer. I don’t know how to coding at all but if this is only way i’m ready to try.

8

Wow, thanks - it worked! Now I wait for the SLI support part :slight_smile:

Anyone from Unreal could please explain how it is going with SLI support?

Cheers!

9

I found something awesome, but I am not sure how to make this work.
Interesting article from NVIDIA about SLI and VR:

And here is a few SDK’s Which can enable SLI support:

I downloaded the VRWorks 1.3 from this link:
https://developer.nvidia.com/gameworksdownload#?search=vr

And here my problem with implementation directory of the SDK begins.

I unziped the package and wasn’t sure which of the files are the important ones and how to install them. I run a demo that is checking if SLI is working. I had somehow 60 fps. I my humble opinion, for a 2x GTX 970 is really poor. After opening my pc in other GPU’s fans were not working. So I assume that SLI is not working at all.

In “NVIDIA Control Panel” in the “Configure SLI, Surround, PhysX” I had a “Maximise 3D performance” option checked and “PhysX settings” set on “CPU”. PC in both settings is detecting both of GPU’s. So the issue is not lack of detect one of the GPU to PC

So I began to contrive. Turned out that in the folder: “C: \ Program Files (x86) \ Epic Games \ 4.10 \ Engine \ Source \ ThirdParty \ NVIDIA \ nvapi” are the same files like this ones in Nvidia package. I replaced them with the ones from “NVAPI-SDK-364.72”. I do not know what to do next. I presume That running this mode requires adding some code.

**- How to run the Nvidia SDK? **

**- How to check that SLI is working? **

10

Days ago I asked one staff who works at Epic Games about SLI (not VR SLI). He said to me that Epic Games doesn’t want to officially make SLI support since it is promoting Nvidia’s hardware. They want to be equal to developers using both Nvidia’s and AMD’s product. So SLI support will not happen in the future at least near future. Also, he mentioned that it is more flexible to contact Nvidia to get their help. I asked about why multi gpu rendering is not supported in Unreal Engine 4. He told me that sometimes it is not Epic Games who doesn’t want it to work. It is just how current engines work. Since SLI works like GPU 1 renders frame 1 and GPU 2 renders frame 2. GPUs are constantly switching. However, while cache from features like SSR and temporal AA is saved in one GPU’s memory and it is not being shared by both GPUs since it is not unified memory. Then SLI works like this:GPU 1 renders 50% and GPU 2 renders 50% or GPU 1 renders 100% while GPU 2 is idle. He added that you can try disabling those features and it will probably give you a boost with dual gpu rig. However, he didn’t remember all the features that using cache in VRAM but I guess they are Temporal AA, SSR, and SSAO. I am not sure about if cascade shadow map uses cache but you can test it if you have dual gpu rig.