A Real-Time Disk Scheduler for Multimedia Integrated Server Considering the Disk Internal Scheduler

The SCSI or the fibre channel (FC) disk drive, called SCSI-FC disk drive has its own internal queue and internal scheduler which maximize its own throughput. The request service order scheduled by the block device drive in Linux is changed by the disk internal scheduler (DIS) and we call this reordering. The conventional real-time disk schedulers are based on Linux block device driver, and the deadlines of the real-time requests are not guaranteed by the reordering of the DIS. This paper proposes a real-time disk scheduling architecture on Linux which solves the reordering problem. It consists of the global scheduler and the local scheduler. The global scheduler selects the real-time requests, predicts their disk I/O times and determines the order based on the spatial locality. The local scheduler is the DIS controlled by the SCSI-FC device driver. The device driver notifies the DIS that the real-time requests with the earlier deadlines must be served before those with the later deadlines. The local scheduler feeds back the measured disk service time to the global scheduler when a requested disk service completes. We have implemented the proposed multimedia disk scheduler on Linux, and the experimental results show that the deadline misses of periodic requests can be reduced up to 19 times (94.7%) by the proposed method.