Abstract: There is no restriction for priority levels in priority scheduling algorithms, which limits the application in practice to get good schedulability. Aiming at that question, considering the requirement of preemptive scheduling for hard real-time systems, a new group priority dynamic real-time scheduling algorithm was presented. The influence of the changed order for some jobs on the schedulability of the system was studied. The schedulability test for the job grouping was given. In the new algorithm, the jobs that satisfied the formula of the schedulability test were joined together as a group. The jobs outside the group schedule in darkest deadline-first, while the jobs in the group schedule in shortest job first. The simulation results show that, comparing with the earliest-dcadlincfirst and other traditional scheduling algorithms, the priority levels decrease deeply, the success ratio increases, the average response time is shorten and the switching number reduces in the new algorithm.

Key words: Mask scheduling, Earliest-deadline-first scheduling algorithm, Success ratio, Switching number