Home arrow BrainDump arrow Page 4 - Linux I/O Schedulers

The CFQ I/O Scheduler - BrainDump

In this sixth part of a seven-part series on the Linux I/O file system, you'll learn about the importance of I/O schedulers, and the various different types. This article is excerpted from chapter four of the book Linux System Programming: Talking Directly to the Kernel and C Library, written by Robert Love (O'Reilly, 2007; ISBN: 0596009585). Copyright © 2007 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.

  1. Linux I/O Schedulers
  2. The Life of an I/O Scheduler
  3. The Deadline I/O Scheduler
  4. The CFQ I/O Scheduler
By: O'Reilly Media
Rating: starstarstarstarstar / 8
December 31, 2008

print this article



The Complete Fair Queuing (CFQ) I/O Scheduler works to achieve similar goals, albeit via a different approach.* With CFQ, each process is assigned its own queue, and each queue is assigned a timeslice. The I/O scheduler visits each queue in a round-robin fashion, servicing requests from the queue until the queue’s timeslice is exhausted, or until no more requests remain. In the latter case, the CFQ I/O Scheduler will then sit idle for a brief period—by default, 10 ms—waiting for a new request on the queue. If the anticipation pays off, the I/O scheduler avoids seeking. If not, the waiting was in vain, and the scheduler moves on to the next process’ queue.

Within each process’ queue, synchronized requests (such as reads) are given priority over nonsynchronized requests. In this manner, CFQ favors reads and prevents the writes-starving-reads problem. Because of the per-process queue setup, the CFQ I/O Scheduler is fair to all processes, while still providing good global performance.

The CFQ I/O Scheduler is well suited to most workloads, and makes an excellent first choice.

The Noop I/O Scheduler

The Noop I/O Scheduler is the most basic of the available schedulers. It performs no sorting whatsoever, only basic merging. It is used for specialized devices that do not require (or that perform) their own request sorting.


>>> More BrainDump Articles          >>> More By O'Reilly Media

blog comments powered by Disqus
escort Bursa Bursa escort Antalya eskort


- Apple Founder Steve Jobs Dies
- Steve Jobs` Era at Apple Ends
- Google's Chrome Developer Tool Updated
- Google's Chrome 6 Browser Brings Speed to th...
- New Open Source Update Fedora 13 is Released...
- Install Linux with Knoppix
- iPad Developers Flock To SDK 3.2
- Managing a Linux Wireless Access Point
- Maintaining a Linux Wireless Access Point
- Securing a Linux Wireless Access Point
- Configuring a Linux Wireless Access Point
- Building a Linux Wireless Access Point
- Migrating Oracle to PostgreSQL with Enterpri...
- Demystifying SELinux on Kernel 2.6
- Yahoo and Microsoft Create Ad Partnership

Developer Shed Affiliates


Dev Shed Tutorial Topics: