–“S” is a function that must be called from within a critical zone and can reschedule internally
–“I” is a function that must be called from within a critical zone and does not reschedule internally
However, in the current documentation there is no explicit mention that S class functions reschedule internally, while no I class functions reschedule. Someone very experienced may be able to infer this from the documentation, but this is something worth mentioning right in the beginning when explaining kernel and API concepts.