An Evaluation of Linux I/O Scheduler Behavior at the Block I/O Layer

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Title: An Evaluation of Linux I/O Scheduler Behavior at the Block I/O Layer
Author: Sinha, Subhas Kumar
Advisors: Dr. Khaled Harfoush, Committee Member
Dr. Xiaohui Gu, Committee Member
Dr. Vincent Freeh, Committee Chair
Abstract: Linux comes with four different I⁄O schedulers - NOOP, Deadline, Anticipatory, and Complete Fairness Queuing (CFQ). Each scheduler attempts to reduce overall response time using different algorithms involving ordering and merging of I⁄O requests. These schedulers tend to behave differently for different types of workloads. In this study we validate the behavior of the different I⁄O schedulers at the block I⁄O layer, present our observations and and give our recomomendation regarding what could be the right scheduler for a particular environment. We have restricted our study to a desktop environment. To capture block I⁄O layer events we use a combination of blktrace (a block I⁄O layer trace tool) and systemtap (a running kernel trace tool). We have captured I⁄O traces for the different schedulers under different application loads. Hard disk queuing effects of SATA⁄ SCSI have an impact on I⁄O behavior and we evaluate this behavior by running our tests on different types of disks. All our tests were run on the ext3 filesystem.
Date: 2008-03-29
Degree: MS
Discipline: Computer Science

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