How to Reduce Delay between Switchboard Instances?

Development Cinematics & Media Virtual Production
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TL;DR There is a delay between scene updates in the switchboard UE Editor and nDisplay instance, I’d love any advice on how to reduce it.

Hey everyone! I’ve run into a roadblock and I’d love any help I can get.

I’m running an LED Wall display, when i launch scenes through switchboard, i have an Editor instance and a nDisplay node. When I, for example, move an object in the editor, it takes ~17ms for that update to reflect on the ndisplay node. I cannot figure out why that delay exists or how to reduce it. (windows ui updates at ~3ms on the same display, for context)

Tech Specs:

  • Ryzen 9950x
  • RTX6000 Workstation
  • 192GB DDR5
  • 10G NIC
  • Unreal 5.7.4
  • Windows 11
  • Virtual Screen: 6144 x 2048 (fed with 2x optical DP 1.4)

Things I’ve already tried:

  • checking for hardware limitations;
    • the rest of the operating system updates on the display close to realtime, so it can’t be the display.
  • I’ve tried super simple scenes with nothing but a cube to rule out scene complexity; same delay occurs
  • Running the display in Lit, Unlit & Wireframe; same delay occurs
  • Changing sync policies in nDisplay; tried them all, same delay occurs
  • Setting the LED display to Low Latency mode; same delay occurs

I’m not really sure what else to try. Even direction on how to troubleshoot would be helpful.

Here’s a video demonstrating the delay(Imgur: The magic of the Internet) (in wireframe view, but the same delay exists regardless of lit/unlit) as well as scene stats from nDisplay; not sure if that maybe has something to do with it?

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21920×1440 495 KB

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11920×1440 665 KB

Any help would be truly appreciated

Thanks <3

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Hello there @MotionStory!

Checking with my peers, the way that delay happens, seems to be exactly when the engine has to swap between editor and nDisplay. Something is taking extra frame time during the swap.

And considering you have already ruled out scene complexity, changing display settings, and adjusting sync policies, I think the cultrip could be outside your UE setup. Since you are working with Win 11, there’s a chance that HAGS is messing up with your frames.

This feature, the Hardware Accelerated GPU Scheduling, has popped around the community from time to time, tied to performance cases. I think it’s worth testing your build without it. To disable it, open your home menu, and type “Graphics”, to reach Graphics settings. On that menu, open the Advanced Graphic Settings, and you will find the toogle for HAGS:

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image634×453 29.7 KB

Disable it, and restart your system. After that, re-open your build, and test if the delay between switchboards is still present.

If the issue persists, you could also test by disabling the engine’s Game Thread, with cmdlet r.OneFrameThreadLag 0. This might result in a general FPS lose, but it should smooth out your boards’ transition.

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Hi @brs-sebascova ! Thanks so much for the reply :slight_smile:

I tried disabling HAGS as well as setting OneFrameThreadLag to 0 for the nDisplay instance.

The same delay still occurs. Out of interest, I also configured the displays to run at 100fps (and the panels at 100Hz) to rule out a framerate limitation, same delay.

I suspect that genlock might solve the issue, so we’re waiting on some genlock equipment to arrive. I’ll post an update here if that solves the issue.