Shared recovery for energy efficiency and reliability enhancements in real-time applications with precedence constraints

While Dynamic Voltage Scaling (DVS) remains as a popular energy management technique for modern computing systems, recent research has identified significant and negative impacts of voltage scaling on system reliability. To preserve system reliability under DVS settings, a number of reliability-aware power management (RA-PM) schemes have been recently studied. However, the existing RA-PM schemes normally schedule a separate recovery for each task whose execution is scaled down and are rather conservative. To overcome such conservativeness, we study in this article novel RA-PM schemes based on the shared recovery (SHR) technique. Specifically, we consider a set of frame-based real-time tasks with individual deadlines and a common period where the precedence constraints are represented by a directed acyclic graph (DAG). We first show that the earliest deadline first (EDF) algorithm can always yield a schedule where all timing and precedence constraints are met by considering the effective deadlines of tasks derived from as late as possible (ALAP) policy, provided that the task set is feasible. Then, we propose a shared recovery based frequency assignment technique (namely SHR-DAG) and prove its optimality to minimize energy consumption while preserving the system reliability. To exploit additional slack that arises from early completion of tasks, we also study a dynamic extension for SHR-DAG to improve energy efficiency and system reliability at runtime. The results from our extensive simulations show that, compared to the existing RA-PM schemes, SHR-DAG can achieve up to 35% energy savings, which is very close to the maximum achievable energy savings. More interestingly, our extensive evaluation also indicates that the new schemes offer non-trivial improvements on system reliability over the existing RA-PM schemes as well.