Why does rebuilding meshes on project open only use one thread?

Development Asset Creation
1

I selected the “city park environment” in my content library, and selected “create new project” from it.
Then I opened 4.26 engine, and selected the CityParkEnvironmentCollec project to open up.
It’s now been building static mesh distance fields for over an hour, stuck at 95% project opening. Tailing the log in Saved/Logs shows that the main work is building distance fields for all the meshes.

However, Process Monitor only shows Unreal Engine using 3.3% of the CPU, which corresponds to a single thread on a 16-core/32-thread CPU.
This feels like work that could be very easily parallelized, so why isn’t it?

2

It depends, if it’s down to the last object then it likely can only build the distance fields on one mesh per thread at a time (like Lightmass) so it might have a big object being built on one thread and it simply takes longer.

3

It’s absolutely just building distance meshes for a bunch of separate objects.


[2021.01.25-18.14.53:344] 0]LogStaticMesh: Built static mesh [41.95s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedBridge03.SM_MergedBridge03
[2021.01.25-18.14.53:770] 0]LogStaticMesh: Building static mesh SM_MergedFence01_1...
[2021.01.25-18.17.03:640] 0]LogStaticMesh: Built static mesh [129.87s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence01_1.SM_MergedFence01_1
[2021.01.25-18.17.06:245] 0]LogStaticMesh: Building static mesh SM_MergedFence01_2...
[2021.01.25-18.19.27:311] 0]LogStaticMesh: Built static mesh [141.07s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence01_2.SM_MergedFence01_2
[2021.01.25-18.19.30:151] 0]LogStaticMesh: Building static mesh SM_MergedFence01_3...
[2021.01.25-18.19.51:526] 0]LogStaticMesh: Built static mesh [21.37s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence01_3.SM_MergedFence01_3
[2021.01.25-18.19.51:943] 0]LogStaticMesh: Building static mesh SM_MergedFence01_4...
[2021.01.25-18.20.44:106] 0]LogStaticMesh: Built static mesh [52.16s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence01_4.SM_MergedFence01_4
[2021.01.25-18.20.45:152] 0]LogStaticMesh: Building static mesh SM_MergedFence01_5...
[2021.01.25-18.21.04:963] 0]LogStaticMesh: Built static mesh [19.81s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence01_5.SM_MergedFence01_5
[2021.01.25-18.21.05:316] 0]LogStaticMesh: Building static mesh SM_MergedFence01_6...
[2021.01.25-18.21.48:569] 0]LogStaticMesh: Built static mesh [43.25s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence01_6.SM_MergedFence01_6
[2021.01.25-18.21.49:492] 0]LogStaticMesh: Building static mesh SM_MergedFence02_4...
[2021.01.25-18.22.12:418] 0]LogStaticMesh: Built static mesh [22.93s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence02_4.SM_MergedFence02_4
[2021.01.25-18.22.12:786] 0]LogStaticMesh: Building static mesh SM_MergedFence02_1...
[2021.01.25-18.22.28:628] 0]LogStaticMesh: Built static mesh [15.84s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence02_1.SM_MergedFence02_1
[2021.01.25-18.22.28:865] 0]LogStaticMesh: Building static mesh SM_MergedFence02_2...
[2021.01.25-18.22.51:455] 0]LogStaticMesh: Built static mesh [22.59s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence02_2.SM_MergedFence02_2
[2021.01.25-18.22.51:834] 0]LogStaticMesh: Building static mesh SM_MergedFence02_3...
[2021.01.25-18.23.10:221] 0]LogStaticMesh: Built static mesh [18.39s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence02_3.SM_MergedFence02_3
[2021.01.25-18.23.10:526] 0]LogStaticMesh: Building static mesh SM_MergedFence03_1...
[2021.01.25-18.23.31:872] 0]LogStaticMesh: Built static mesh [21.35s] /Game/CityPark/Meshes/MergeMeshes/SM_MergedFence03_1.SM_MergedFence03_1
[2021.01.25-18.23.32:241] 0]LogStaticMesh: Building static mesh SM_MergedFence03_2...

Interspersed with shader compilation.

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