Modelling Restricted Processor Sharing.
Feng Zhang, Lester Lipsky · 2006
In principle unrestricted processor sharing can be very useful when jobs with widely varying CPU requirements are competing for the same processor. Even if there are several processors available, processor sharing can be useful. However, in practice it must be implemented by round-robin, and there is an overhead cost (e.g., cache thrashing) to implementing this scheme. Furthermore, the overhead may depend on the number of jobs that are active, and can be significant. Therefore restricted processor sharing, which only allows a limited number of jobs to share the processors, may be a more appropriate strategy. In this paper we present a comprehensive analytic model to study the interplay among the number of parallel processors, the maximum degree of processor sharing, the overhead, and the job arrival rate. We examine how the CPU time distribution affects mean system time (or response time), under what conditions two slow processors are better than one double fast one, and when it pays to invoke restricted processor sharing.