Guaranteed task deadlines for fault-tolerant workloads with conditional branches

This work examines scheduling for a real-time multiprocessor (MAFT) in which both hard deadlines and fault-tolerance are necessary system components. A workload for this system consists of a set of concurrent dependent tasks, each with some execution frequency; tasks are also fully ordered by priority. Fault tolerance mechanisms include hardware-supported voting on computation results as well as on task starts, task completions, and branch conditions. The distributed agreement mechanism used on system-level decisions adds a variable threading delay to the run time of each copy of a task. These delays make current schedule verification techniques inapplicable. In the most general execution profile, each processor in the system runs a subset of the tasks, with different tasks possibly having different frequencies. In this work, however, we restrict attention to a special class of workloads, termed uni-schedule, in which each processor executes the entire task set, using the multiple processors to implement full redundancy. In addition, all tasks are assumed to have the same periodicity. Given these restrictions, we produce stable schedules consistent with the initial workload specifications. Algorithms are first given for uni-schedule workloads with no run-time branches, and then for uni-schedule workloads with branches.