An analysis of decay-usage scheduling in multiprocessors

Abstract

Priority-ageing or decay-usage scheduling is a time-sharing scheduling policy capable of dealing with a workload of both interactive and batch jobs by decreasing the priority of a job when it acquires CPU time, and by increasing its priority when it does not use the (a) CPU. In this paper we deal with a decay-usage scheduling policy in multiprocessor systems modeled after widely used systems. The priority of a job consists of a base priority and a time-dependent part based on processor usage. Because the priorities in our model are time dependent, a queueing-theoretic analysis, for instance for the mean response time, seems impossible. Still, it turns out that as a consequence of the scheduling policy, the shares of available CPU time obtained by jobs converge, and a deterministic analysis for these shares is feasible: for a fixed set of jobs with very large (infinite) processing demands, we derive the relation between their base priorities and their steady-state shares. In addition, we analyze the relation between the values of the parameters of the scheduler and the level of control it can exercise over the steady-state shares. We validate the model by simulations and by measurements of actual systems.