Utility Accrual Real-Time Scheduling Under Variable Cost Functions

We present a utility accrual real-time scheduling algorithm called CIC-VCUA, for tasks whose execution times are functions of their starting times (and potentially other factors). We model such variable execution times using variable cost functions (or VCFs). The algorithm considers application activities that are subject to time/utility function time constraints, execution times described using VCFs, and mutual exclusion constraints on concurrent sharing of non-CPU resources. We consider the two-fold scheduling objective of (1) assure that the maximum interval between any two consecutive, successful completions of job instances in an activity must not exceed the activity period (an application-specific objective), and (2) maximizing the system’s total accrued utility, while satisfying mutual exclusion resource constraints. Since the scheduling problem is intractable, CIC-VCUA is a polynomial-time heuristic algorithm. The algorithm statically computes worst-case task sojourn times, dynamically selects tasks for execution based on their potential utility density, and completes tasks at specific times. We establish that CIC-VCUA achieves optimal timeliness during under-loads, and tightly upper bounds interand intra-task completion times. Our simulation experiments confirm the algorithm’s effectiveness and superiority.