Summary: Li, Wenming, Group-EDF - a new approach and an efficient non-preemptive
algorithm for soft real-time systems. Doctor of Philosophy (Computer Science),
August 2006, 123 pp., 6 tables, 49 illustrations, references, 48 titles.
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