Spawning entity prefabs via EM is much slower than subscene

I've always used subscenes and put my predefined prefabs there, but now I need to spawn some on the fly. And to my surprise it takes waaay too long to spawn an Entity prefab with ~100k children entities, EntityManager.Instantiate takes around 200ms on my PC and ~500ms on Android. The same prefab being put into an empty SubScene loads up instantly. I cook my prefabs the usual way with DeclareReferencedPrefabs and store static reference to an entity, and I can inspect it in the debugger for sure (so it is converted). Am I doing smth wrong? Should be exactly the same performance both the DeclareReferenced+Instantiate and SubScene ways.

 

This might help.

 

This post describes the standard DeclareReferencedPrefabs path.

To answer my own original question, here's the quote from Unity docs: "When you save a scene, Unity converts any Sub Scenes to a native, binary format. This format is memory-ready and can be loaded or streamed with only minimal alteration of the data in RAM. The format is ideally suited for streaming large amounts of Entities."

So memory layout is the key difference between just storing a prefab and storing it and/or using a SubScene. Sounds like it's the best solution for prefabs containing 100k+ entities, and definitely the only feasible way for 1M+ entities.

I've tested the following methods:
- store actual prefab in a subscene, instantiate as usual
- store a normal set of entities in a subscene and manually assign Prefab tag, instantiate as usual
- store a normal set of entities in a subscene and instantiate with SceneLoadFlags.NewInstance

First two make no difference, though the last one is blazing fast, requires some boilerplate to address the newly instantiated prefab, but unfortunately either buggy or I am missing something. Like it won't unload all copies of a subscene on sceneSystem.UnloadScene()

 

Thanks for the clarification!

And yes, I'm instantiating millions of particles. Assembling such prefabs brings the editor to its knees, but that's another problem. At least the instantiation part is clear now, hope the subscenes instantiation will help.