schedulability

Schedulability refers to the capability of a set of real-time tasks to meet all timing requirements when executed on a given computing platform under a specified scheduling algorithm. It is a central concern in real-time systems, where missing a deadline can be as unacceptable as failing to produce correct results.

Task models typically specify each task by its worst-case execution time (WCET), period or minimum inter-arrival time, and relative deadline (often equal to the period). Tasks may be periodic or sporadic, and scheduling can be preemptive or non-preemptive. Multitask systems may run on a single processor or on multiple processors, with partitioned, global, or mixed scheduling approaches.

Common scheduling algorithms include fixed-priority methods such as rate monotonic scheduling (RMS) and earliest deadline first (EDF). In uniprocessor systems, RMS provides a utilization-based bound on schedulability, given by U ≤ n(2^{1/n} − 1). EDF allows a utilization bound of up to 1.0 for tasks with deadlines equal to periods. For multiprocessors, schedulability becomes more complex and often requires different analyses or heuristics, as the problem is generally NP-hard.

Analytical methods to test schedulability include response-time analysis, time-demand analysis, and other exact or sufficient tests. These analyses typically assume worst-case execution times and may be conservative. In practice, schedulability analysis informs design decisions such as task partitioning, period selection, and the choice of scheduling algorithm to ensure timing guarantees for real-time applications.