Inquiry on Multi-GPU Rendering and Output with nDisplay

Development Cinematics & Media Virtual Production
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1

In a single computer with multiple GPUs, where internal in-camera views are not required and only the out-camera output is needed:

  • Under a 4-GPU setup, is it possible to output 4K through the output port of just one GPU, while each of the 4 GPUs renders an HD view separately?

Additionally, on one computer, what is the maximum number of GPUs that nDisplay can support? For example, would rendering with 8 or even 12 GPUs be feasible?

2

Hello Haigen,

nDisplay has two options in that regard:

  • MGPU (former SLI), and this method is not recommended due to a variety of potential rendering issues
  • Multi Process Rendering, which has excellent documentation - Multi-Process Rendering | Course

Both methods require specialized hardware that supports fast PCI transfers to facilitate, and have not been tested for more than 2 GPUs

4 GPUs in case Multi Process Rendering means four application instances on a single machine, which could be too heavy for the CPU to handle, or might require a CPU with high core numbers. We recommend considering the 2110 workflow to spread the load across multiple computers https://dev.epicgames.com/documentation/en\-us/unreal\-engine/setting\-up\-smpte\-2110\-in\-unreal\-engine?application\_version\=5\.6\#setting\-up\-smpte\-2110\-in\-unreal\-engine

3

Hello Boiko,

Thank you for your explanation and the documentation links. I’ve conducted some tests regarding CPU hyper-threading and multi-GPU performance.

  • With hyper-threading disabled, FPS improves, but scaling to 4 GPUs still shows other limitations.
  • Test results:
    • 4 GPUs (3840×2160) → 40–48 FPS (HT disabled), 18–20 FPS (HT enabled)
    • 3 GPUs (5760×1080) → 57–60 FPS (HT disabled), 49–56 FPS (HT enabled)

From these results, it seems disabling hyper-threading has a clear effect, but performance still does not reach 60 FPS with 4 GPUs.

May I ask if there are any other possible causes or solutions that could help improve 4-GPU performance?

4

Hello Haigen,

it would be great to look into the traces to get a better idea of performance.

UE has a great profiler to capture performance traces - https://dev.epicgames.com/documentation/en-us/unreal-engine/unreal-insights-reference-in-unreal-engine-5

https://dev.epicgames.com/documentation/en-us/unreal-engine/unreal-insights-overview-in-unreal-engine

Could you please capture the test session (~30sec) and upload for us to look into?

You can start capture by console command “Trace.Start cpu, gpu, frame” and stop by “Trace.Stop”

Files are stored under Saved/Profiling folder in the project.

Thank you,

vitalii