Assignment and Scheduling: Many Classes and Processors

This chapter concerns the problem of scheduling service in multiclass and multiprocessor systems, and discusses key ideas in recent work in this area. The possibility of effective treatment of multiclass problems enlarges the scope of applications considerably. There will be no switchover time or cost or processor interruption. Sections 5.3 and 6.4 dealt with some specific multiclass systems, but where the priorities were fixed beforehand. Those examples well illustrated the considerable advantages of the workload formulation. The advantages of the workload formulation were also seen in Chapter 11, which dealt with scheduling problems for simpler systems, but where many of the basic issues (averaging theorems, switchover time, vacations) were different. A significant advantage of the workload formulation in Sections 5.3 and 6.4 was that the workload did not (at least asymptotically) depend on the priorities. It was well behaved and did not exhibit the rapid movement of the individual queues. In this sense the workload was an “invariant” of the system. The advantages of the workload formulation for multiclass systems will also be apparent for the classes of problems in this chapter.