A Scheduling Framework That Makes Any Disk Schedulers Non-Work-Conserving Solely Based on Request Characteristics

Exploiting spatial locality is critical for a disk scheduler to achieve high throughput. Because of the high cost of disk head seeks and the non-preemptible nature of request service, state-of-the-art disk schedulers consider the locality of both pending and future requests. Though schedulers adopting the approach, such as the anticipatory scheduler, show substantial performance advantages, they need to know from which processes requests are issued to evaluate locality. This approach is not effective when the knowledge about processes is not available (e.g., in virtual machine environment, network or parallel file systems, and SAN) or the locality exhibited on a disk region is not solely determined by individual processes (e.g., in the case of cooperative process groups and disk array where requested data are striped). We propose a light-weight disk scheduling framework that does not require any process knowledge for analyzing request locality. Solely based on requests’ own characteristics the framework can make any work-conserving scheduler non-work-conserving, i.e., able to take future requests as dispatching candidates, to fully exploit locality. Additionally, we show how to effectively extend the framework to the disk array environment. Our design, Stream Scheduling, is prototyped in the Linux kernel 2.6.31. With extensive experiments of representative benchmarks, and in various environments such as the Xen virtual machine and the PVFS parallel file system, we show that the proposed scheduling framework can improve their performance by up to 3.2 times.