However, the history of their being together comes from
9bebe9e5b0f3 ("kbuild: Fix .text.unlikely placement")
which seems to indicate there was some problem with having them separated out, although I don't quite understand what the issue was from the commit message.
Separating it out is less efficient. Gives worse packing for the hot part if they are not aligned to 64byte boundaries, which they are usually not.
It also improves packing of the cold part, but that probably doesn't matter.
-Andi