SIGMETRICS '93 Proceedings of the 1993 ACM SIGMETRICS conference on Measurement and modeling of computer systems
A non-preemptive scheduling algorithm for soft real-time systems
Computers and Electrical Engineering
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In this work, we introduce a real-time task model, where tasks receive a ``reward'''' that depends on the amount of service received. In this model, tasks have associated deadlines at which they must depart from the system. The task computations are such that the longer they are able to execute before their deadline, the greater the value of their computations, i.e., the tasks have the property that they receive increasing reward with increasing service (IRIS). We focus on the problem of scheduling IRIS tasks in a system in which tasks arrive randomly over time, with the goal of maximizing the average reward accrued per task and per unit time. We describe and evaluate a two-level policy for this system. A top-level algorithm executes each time a task arrives and determines the amount of service to allocate to each task in the absence of future arrivals. A lower-level algorithm, an earliest deadline first (EDF) policy in our case, is responsible for the actual selection of tasks to execute. This two-level policy is evaluated through a combination of analysis and simulation. We observe that it provides nearly optimal performance when the variance in the interarrival times and/or laxities is low and that the performance is more sensitive to changes in the arrival process than the deadline distribution. The work reported in this paper was supported by ONR grant N00014- 87-K-0796 and by NSF grant CCR-9119922.