Value-Driven Multi-Class Overload Management

While it is imperative that all time constraints are met in hard real-time systems, firm or soft real-time systems do not have as stringent timeliness requirements, allowing for some degree of tardiness (soft) or miss ratio (firm). A significant body of research within the soft and firm real-time area has focused on minimizing tardiness and/or miss ratio, but without quantifying acceptable levels. In this paper, we focus on scheduling of multi-class transaction workloads, where the workload consists of transaction classes having firm transactions, where firm transaction classes have additional requirements specifying the minimum acceptable completion ratios that should be met in order to maintain system correctness. We present a value-driven overload management algorithm with a bias control mechanism, called OR-ULD/BC, which attempts to bias the execution among transaction classes such that minimum completion ratio constraints are satisfied. The performance analysis shows that OR-ULD/BC enforces transaction class timeliness requirements within a specified operational envelope.