Having only dealt with this at the level of writing code for a RISC microcontroller, another facet I don't see mentioned that may be of importance is the follow

Having only dealt with this at the level of writing code for a RISC microcontroller, another facet I don't see mentioned that may be of importance is the following CPU implementation detail. Code compiles to assembly instructions which typically appear atomic to the author, however, such instructions may take variable numbers of cycles to execute.