the thing is: codegen-units defaults to 16 in release builds, and by far the most time in the "passes" list is spend in LLVM passed (which is was codegen-units

the thing is: codegen-units defaults to 16 in release builds, and by far the most time in the "passes" list is spend in LLVM passed (which is was codegen-units parallelizes),so most times it shouldn't be stuck with 1 high load core (even if it's not 16 all the time). so it looks a lot like something is prevented the intended codegen parallelization of the crate Through it indeed might not have been a bug, e.g. before the change in generation to split it across crates source code might have been in a way where it can't split the crate into multiple units. Or maybe something made rust believe splitting it is a bad idea, e.g. related to memory usage or similar.