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Eliminating Request Starvation due to Expectation Discrepancy between NCQ and I/O Scheduler  

Yu, Young-Jin (서울대학교 전기컴퓨터공학)
Shin, Dong-In (서울대학교 전기컴퓨터공학)
Jung, Im-Young (서울대학교 전기컴퓨터공학)
Yeom, Heon-Young (서울대학교 전기컴퓨터공학)
Publication Information
Journal of KIISE:Computing Practices and Letters / v.15, no.5, 2009 , pp. 400-404 More about this Journal
Abstract
Native Command Queueing is a technology to maximize throughput of disk system by reordering requests in its command queue. Recent S-ATA 2 standard specifies a protocol for the purpose of dealing with NCQ feature, making most vendors implementing it in their disk devices. However, the new feature, NCQ, may lead to information gap between OS and disk drive. 05 considers that disk will service I/O requests in the order as OS has dispatched. Unfortunately, it isn't true any more since NCQ would simply ignore the policy of OS and reorder the sequence OS has expected. Let us define the term as expectation-discord. Due to the discord, serious performance anomalies or starvation of requests may occur in I/O subsystem. In this paper, we confirm that the expectation-discord actually brings about starvation of requests. We propose a solution to settle it. Our solution is very simple, effective, cheap(not requiring any hardware modification) and portable across various OS. Experimental results show that our solution can balance throughput and response time very well.
Keywords
I/O scheduler; NCQ; expection-discord; starvation;
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