Scheduling Parallel Real-Time Recurrent Tasks on Multicore Platforms

We consider the scheduling of a real-time application that is modeled as a collection of parallel and recurrent tasks on a multicore platform. Each task is a directed-acyclic graph (DAG) having a set of subtasks (i.e., nodes) with precedence constraints (i.e., directed edges) and must complete the execution of all its subtasks by some specified deadline. Each task generates potentially infinite number of instances where the releases of consecutive instances are separated by some minimum inter-arrival time. Each DAG task and each subtask of that DAG task is assigned a fixed priority. A two-level preemptive global fixed-priority scheduling (GFP) policy is proposed: a task-level scheduler first determines the highest-priority ready task and a subtask-level schedulerthen selects its highest-priority subtask for execution. To our knowledge, no earlier work considers a two-level GFP scheduler to schedule recurrent DAG tasks on a multicore platform. We derive a schedulability test for our proposed two-level GFP scheduler. If this test is satisfied, then it is guaranteed that all the tasks will meet their deadlines under GFP. We show that our proposed test is not only theoretically better but also empirically performs much better than the state-of-the-art test in scheduling randomly generated parallel DAG task sets.