Thread_pool.PriorityPriority.t is what is usually referred to as the "nice" value of a process. It is also known as the "dynamic" priority. It is used with normal (as opposed to real-time) processes that have static priority zero. See Unix.Scheduler.set for setting the static priority.
type t = Linux_ext.Priority.tinclude Sexplib0.Sexpable.S with type t := tinclude Sexplib0.Sexpable.Of_sexp with type t := tval t_of_sexp : Sexplib0.Sexp.t -> tinclude Sexplib0.Sexpable.Sexp_of with type t := tval sexp_of_t : t -> Sexplib0.Sexp.tval of_int : int -> tval to_int : t -> int