Impact of bus arbitration on the schedulability of real-time shared-bus multiprocessors

One of the underestimates in schedulability analysis of bus-based real-time multiprocessors is the impact of the system bus. The system bus is a source of schedulability loss (caused by the bus interference) as well as a shared resource. In this paper, we first identify the factors that impact on the system bus on schedulability as being (a) management of the task priorities at the bus interface and (b) the bus arbitration policy. We then investigate the impact of the waiting time of each task required to use the system bus on the schedulability for different numbers of processors and various memory request rates. Analysis results based on a discrete-time Markov chain show that when the memory request rate of each processor is less than 16%, the impact of the waiting time is negligible; otherwise, the waiting time must be taken into account in schedulability analysis. The number of processors supportable without schedulability violation and the impact on the schedulability bound are also shown