GSR: A global seek-optimizing real-time disk-scheduling algorithm

Earliest-deadline-first (EDF) is good for scheduling real-time tasks in order to meet timing constraint. However, it is not good enough for scheduling real-time disk tasks to achieve high disk throughput. In contrast, although SCAN can maximize disk throughput, its schedule results may violate real-time requirements. Thus, during the past few years, various approaches were proposed to combine EDF and SCAN (e.g., SCAN-EDF and RG-SCAN) to resolve the real-time disk-scheduling problem. However, in previous schemes, real-time tasks can only be rescheduled by SCAN within a local group. Such restriction limited the obtained data throughput. In this paper, we proposed a new globally rescheduling scheme for real-time disk scheduling. First, we formulate the relations between the EDF schedule and the SCAN schedule of input tasks as EDF-to-SCAN mapping (ESM). Then, on the basis of ESM, we propose a new real-time disk-scheduling algorithm: globally seek-optimizing rescheduling (GSR) scheme. Different from previous approaches, a task in GSR may be rescheduled to anywhere in the input schedule to optimize data throughput. Owing to such a globally rescheduling characteristic, GSR obtains a higher disk throughput than previous approaches. Furthermore, we also extend the GSR to serve fairly non-real-time tasks. Experiments show that given 15 real-time tasks, our data throughput is 1.1 times that of RG-SCAN. In addition, in a mixed workload, compared with RG-SCAN, our GSR achieves over 7% improvement in data throughput and 33% improvement in average response time.