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| PASS: a simple, efficient parallelism-aware solid state drive I/O scheduler |
| Hong-yan Li, Nai-xue Xiong, Ping Huang, Chao Gui |
| Wuhan National Laboratory for Optoelectronics, School of Computer Science and Technology, Huazhong University of Science and Technology, Wuhan 430070, China; School of Information Management, Hubei University of Economics, Wuhan 430205, China; School of Computer Science, Colorado Technical University, Colorado Spring, CO 80907, USA |
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Abstract Emerging non-volatile memory technologies, especially flash-based solid state drives (SSDs), have increasingly been adopted in the storage stack. They provide numerous advantages over traditional mechanically rotating hard disk drives (HDDs) and have a tendency to replace HDDs. Due to the long existence of HDDs as primary building blocks for storage systems, however, much of the system software has been specially designed for HDD and may not be optimal for non-volatile memory media. Therefore, in order to realistically leverage its superior raw performance to the maximum, the existing upper layer software has to be re-evaluated or re-designed. To this end, in this paper, we propose PASS, an optimized I/O scheduler at the Linux block layer to accommodate the changing trend of underlying storage devices toward flash-based SSDs. PASS takes the rich internal parallelism in SSDs into account when dispatching requests to the device driver in order to achieve high performance. Specifically, it partitions the logical storage space into fixed-size regions (preferably the component package sizes) as scheduling units. These scheduling units are serviced in a round-robin manner and for every chance that the chosen dispatching unit issues only a batch of either read or write requests to suppress the excessive mutual interference. Additionally, the requests are sorted according to their visiting addresses while waiting in the dispatching queues to exploit high sequential performance of SSD. The experimental results with a variety of workloads have shown that PASS outperforms the four Linux off-the-shelf I/O schedulers by a degree of 3% up to 41%, while at the same time it improves the lifetime significantly, due to reducing the internal write amplification.
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Received: 16 September 2013
Published: 06 May 2014
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PASS：一种简单、高效、并行感知的固态盘I/O调度器
研究目的：随着半导体技术的日益成熟，基于半导体技术的固态盘被越来越多地应用到存储系统。然而，由于固态盘与机械式磁盘性能特征不同，现有的面向机械式磁盘的软件不能充分利用固态盘的独有特性，影响固态盘的性能发挥。现有Linux内核中的块层I/O调度器都是面向机械式磁盘的，因此，本文提出一种优化的、充分利用固态盘内部丰富并行性的I/O调度器--PASS。
创新要点：利用SSD底层丰富的内部特征，指导上层软件的设计和实现更好协同性能。特别是，利用其内部丰富的并行性实现了一个简单、高效的固态硬盘I/O调度器作为Linux内核模块，可以替代块层的I/O调度器集成到内核中工作。其性能优于现有的I/O调度器，同时提高了SSD寿命。
方法提亮：将逻辑存储空间分成若干固定大小的区域，并以区域为调度单位轮流调度。每次发送请求时只向区域发送与其内部并行性相匹配的请求数量，避免发送过多请求，引起性能下降。并且，将读、写请求分开，避免相互干扰。
重要结论：针对固态盘内部丰富的并行性，优化设计块层I/O调度器PASS，有针对性地在内核I/O调度层进行优化，充分利用了固态盘内部并行操作单元之间和单元之内的并行性。基于多种工作负载的实验表明，PASS在性能上优于Linux内核中现有的四种I/O调度器。
关键词：
固态盘,
I/O调度器,
并行性
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