Processor sharing or egalitarian processor sharing is a service policy where the customers, clients or jobs are all served simultaneously, each receiving an equal fraction of the service capacity available.
[1] The sojourn time jobs experience has no closed form solution, even in an M/M/1 queue.
[3] Generalized processor sharing is a multi-class adaptation of the policy which shares service capacity according to positive weight factors to all non-empty job classes at the node, irrespective of the number of jobs of each class present.
All practical schedulers approximate GPS and use it as a reference to measure fairness.
"[4] In multilevel processor sharing a finite set of thresholds are defined and jobs partitioned according to how much service they have received.