Task Splitting and Load Balancing of Dynamic Real-Time Workloads for Semi-Partitioned EDF

Many real-time software systems, such as those commonly found in the context of multimedia, cloud computing, robotics, and real-time databases, are characterized by a dynamic workload, where applications can join and leave the system at runtime. Global schedulers can transparently support dynamic workload without requiring any off-line task-allocation phase, thus providing advantages to the system designer. Nevertheless, such schedulers exhibit poor worst-case performance when compared to semi-partitioned schedulers, which instead can achieve near-optimal schedulability performance when used in conjunction with smart task splitting and partitioning techniques, and they are also lighter in terms of run-time overhead. This article proposes an approach to efficiently schedule dynamic real-time workloads on multiprocessor systems by means of semi-partitioned scheduling. A linear-time approximation scheme for the C=D splitting algorithm under partitioned EDF scheduling is proposed. Then, a load-balancing algorithm is presented to admit new real-time workloads with a limited number of re-allocations. The article finally reports on a large-scale experimental study showing that (i) the linear-time approximation is characterized by a very limited utilization loss compared with the corresponding exact approach (that has a much higher complexity), and that (ii) the whole approach allows achieving considerable improvements with respect to global and partitioned EDF scheduling.