A Real-Time Scheduling Algorithm for Soft Periodic Tasks

Since now, some scheduling algorithms have been presented to guarantee the time constraints of soft real-time tasks, but most of them have some drawbacks. The first drawback of them is that scheduling decisions are based on parameters which are assumed to be crisp; however, in many environments the values of these parameters are uncertain. The second one is the high time complexity of these methods. In this paper, a new soft real time scheduling algorithm, called Maximum Miss First (MMF), is proposed to overcome some of these disadvantages. MMF determines priority of tasks according to their miss ratios. The miss ratios of all the system tasks are approximately equal when MMF is used. Because miss ratio affects other QoS parameters, using MMF is suitable for systems that need similar QoS for its tasks even in overrun and overload conditions. To evaluate MMF, its performance was compared with the EDF algorithm as well as three recent works in this context (gEDF, RLP and RD-EDF) by simulation. Simulation results showed that MMF generally outperformed the EDF, RD-EDF, RLP, and gEDF in terms of system utilization, output jitter, and fairness, but gEDF had higher success ratio because it tends to service smaller jobs. The time complexity of proposed method is near to EDF.