Multimedia real-time disk scheduling by hybrid local/global seek-optimizing approaches

Real-time disk scheduling is one of the most important problems in designing a multimedia system. It has been proved to be NP-complete. Recently, various approaches have been proposed to improve disk throughput under guaranteed real-time requirements. SCAN-EDF, which scans the disk surface to retrieve the task data block under the disk head in order to re-schedule tasks in a real-time EDF (earliest deadline first) schedule, is one of the best-known real-time disk scheduling methods. Since tasks rescheduled in SCAN-EDF should have the same deadline, its efficiency depends on the number of tasks with the same deadline. If all tasks have different deadlines, the scheduling results of SCAN-EDF would be the same as EDF. In this paper, we improve SCAN-EDF by applying different hybrid local-merging and global-inserting schemes. As opposed to SCAN-EDF, in our method tasks rescheduled by SCAN may have different deadlines. Its efficiency is not limited by the number of tasks that have the same deadlines. Experiments show that the proposed method is significantly better than SCAN-EDF. In terms of disk throughput, the improvement obtained is 24% greater than the best-known SCAN-EDF method.