schedulabilitydokumentation

Schedulability is a property of a real-time system describing whether a given set of tasks can be scheduled so that all timing constraints are met under a particular scheduling algorithm and hardware model. Tasks typically have attributes such as execution time, period or arrival pattern, and relative deadline. The goal of schedulability analysis is to determine, without exhaustive simulation, whether every task can complete before its deadline for all possible executions.

Schedulers may be fixed-priority, such as rate-monotonic (RM) and deadline-monotonic (DM), or dynamic, such as earliest-deadline first (EDF). Schedulability tests include utilization-based bounds, response-time analysis, and time-demand analysis. A common result is that simple utilization bounds provide sufficient but not necessary conditions. For example, with fixed priorities and implicit deadlines, the classical Liu-Layland bound gives a safe utilization limit that depends on the number of tasks; as the number of tasks grows, the bound approaches about 0.69. More precise tests compute worst-case response times or worst-case demand to decide schedulability exactly.

Real-time schedulability must consider practical factors beyond the abstract model. Preemption costs, blocking due to shared resources, and priority inversion can reduce schedulability. In multiprocessor systems, schedulability analysis is more complex, with partitioned and global scheduling approaches and additional coordination protocols. Schedulability analysis is widely used in safety-critical domains to verify that timing requirements are met, and it informs design decisions such as task partitioning, slowdown allowances, or alternative algorithms.