ELF Priority Policy

We define the class of "EDF-Like-within-Fixed-priority (ELF)" scheduling policies. ELF scheduling is a (large) subset of the class of JLFP scheduling policies that can be structurally viewed as a combination of fixed-priority and GEL scheduling policies. In ELF scheduling, we take an FP policy as an argument, and each task has a constant "priority-point offset." Each job's absolute priority point is given by its arrival time plus its task's priority-point offset. Given two jobs, their relative priority order is first determined by the fixed-priority policy, i.e., the priority order of their respective tasks. If their tasks have equal fixed priority, then it is determined by the jobs' priority points, with the interpretation that an earlier priority point implies higher priority. We define what it means for an abstract job-level fixed-priority policy to behave as an ELF policy.

Consider any type of tasks ...

... and jobs of these tasks with absolute priority points.

Given an underlying FP policy, a JLFP policy is ELF if it never inverts task-level priority, and, among equal-priority tasks, never inverts priority-point order. Ties among jobs with equal task priority and equal priority points may be resolved by any reflexive, transitive, and total tie-breaking rule.