I actually thought this too, but I noticed the “comments” in the BaseEngine.ini file are actually written ABOVE the entry they are referring to, so the following comments (and their corresponding default values) should be read as such:
; Make sure we don’t starve loading threads
NumUnusedShaderCompilingThreads=3
; Make sure the game has enough cores available to maintain reasonable performance
NumUnusedShaderCompilingThreadsDuringGame=4
; Core count threshold. Below this amount will use NumUnusedShaderCompilingThreads. Above this threshold will use PercentageUnusedShaderCompilingThreads when determining the number of cores to reserve.
ShaderCompilerCoreCountThreshold=12
; Percentage of your available logical cores that will be reserved and NOT used for shader compilation
; 0 means use all your cores to compile Shaders
; 100 means use none of your cores to compile shaders (it will still use 1 core).
PercentageUnusedShaderCompilingThreads=50
; Batching multiple jobs to reduce file overhead, but not so many that latency of blocking compiles is hurt
MaxShaderJobBatchSize=10
; Set process priority for ShaderCompileWorker (0 is normal)
WorkerProcessPriority=-1
(Warning: Raising the WorkerProcessPriority from its default of below normal (-1) may cause your system to freeze if you have too many threads dedicated to shader compilation!)