Using Prioritized Disk Service to Expedite Program Execution

Computer systems often host multiple programs in execution simultaneously. Among those running programs, some may be important and time-critical, which users would expect them to finish their execution as soon as possible. Generally speaking, the course of program execution includes CPU operation and hard disk operation (disk I/O). For the CPU operation, modern computer systems have the ability to adjust the CPU scheduling sequence according to program priority. However, most computer systems do not have effective ways to conduct disk I/O based on program priority. The Linux operating system has been widely used in many areas. It supports several disk schedulers. The Complete Fair Queuing (CFQ) and the Anticipatory Scheduling (AS) are among those most well-known. Currently, CFQ is the default disk scheduler in the Linux operating system. AS is the predecessor of CFQ. Unfortunately, CFQ only offers prioritized disk I/O to some extent through the tool "ionice", while AS does not provide any prioritized service at all. We propose and implement a new disk scheduler, namely Prioritized Anticipatory Scheduling (PAS), by adding schemes of supporting prioritized disk I/O into AS in the Linux kernel. Our experimental results show that PAS surpasses CFQ with ionice for the vast majority of all test cases. Compared with AS, PAS can improve the performance of programs with high disk I/O priority by up to 71.88%.