Group Edf – a New Approach and an Efficient Non-preemptive Algorithm for Soft Real-time Systems

Group-EDF-a new approach and an efficient non-preemptive algorithm for soft real-time systems. Hard real-time systems in robotics, space and military missions, and control devices are specified with stringent and critical time constraints. On the other hand, soft real-time applications arising from multimedia, telecommunications, Internet web services, and games are specified with more lenient constraints. Real-time systems can also be distinguished in terms of their implementation into preemptive and non-preemptive systems. In preemptive systems, tasks are often preempted by higher priority tasks. Non-preemptive systems are gaining interest for implementing soft-real applications on multithreaded platforms. In this dissertation, I propose a new algorithm that uses a two-level scheduling strategy for scheduling non-preemptive soft real-time tasks. Our goal is to improve the success ratios of the well-known Earliest Deadline First (EDF) approach when the load on the system is very high and to improve the overall performance in both underloaded and overloaded conditions. Our approach, known as group-EDF (gEDF), is based on dynamic grouping of tasks with deadlines that are very close to each other, and using a Shortest Job First (SJF) technique to schedule tasks within the group. I believe that grouping tasks dynamically with similar deadlines and utilizing secondary criteria, such as minimizing the total execution time can lead to new and more efficient real-time scheduling algorithms. I present results comparing gEDF with other real-time implemented gEDF algorithm in the Linux kernel and evaluated gEDF for scheduling real applications. ACKNOWLEDGEMENTS First, I am deeply grateful to Dr. Kavi, my major professor, for his consistent assistance and brilliant supervision since 2002. Without which, I would not have achieved significant progress. He enlightened me to choose a new approach that I initially used in developing a real-time extension of the Scheduled Dataflow Architecture. He encouraged me to develop the innovative idea into a complete real-time algorithm. I would like to thank Dr. Akl for providing the modeling and simulation tools, and his participation in weekly research meetings for the last three years. I would like to thank Dr. Akl and Dr. Sweany for their suggestions and supervision on my doctoral study and dissertation. given me much help since 1999. Last but not least, I owe my parents, my wife, and my daughter so much. I particularly thank them for their strong support during these years. Figure 3.1-4: (a) Four jobs with different deadlines. (b) EDF Scheduling with FIFO when soft tolerance is allowed. …