Mutli GPU Pathtracing Dirty Geometry Crashing

Development Rendering
1

Hi,

I have a multi GPU setup - 2 x A6000 GPUs set up with NVLINK and following Alex Pearce’s video tutorial ( (64) Multi-GPU Tutorial in Unreal Engine! - YouTube) - but I have a crash every time I start the pathtracer on one of my projects. Runs fine on just one GPU with Pathtracing. Unreal 5.3.2

Assertion failed: !Geometry->IsDirty(CommandContext.GetGPUIndex()) [File:D:\build++UE5\Sync\Engine\Source\Runtime\D3D12RHI\Private\D3D12RayTracing.cpp] [Line: 4134] Acceleration structures for all geometries must be built before building the top level acceleration structure for the scene.

I have tried a blank project and added one by one all the plugins we are using and then added Megascans and our own geometry and I can get it all working fine.

The problem is on a large existing project I have this crash every time I swap to pathtracing. Is there any way of troubleshooting this error so I can work out what may be causing the issue? How do I build acceleration structures for all geometries?

Thanks for any guidance.

2

I also have a 2 x A6000 w/ NVLINK setup, and am experiencing the exact same crash and error message when trying to start Path Tracing in a rather complex scene. Path Tracing does work fine in an empty new map within the same project though, so it seems like it’s geometry-dependent and not related to a plugin mismatch or config issue. For now, I’m kinda giving the metahumans a suspicious side-eye - but may also test without Nanite enabled.

4

We are not using Metahumans - so probably not that - but we are using Nanite. I guess we could try turning it all off - by command and see if that helps.