Noop scheduler

The NOOP scheduler is the simplest I/O scheduler for the Linux kernel. This scheduler was developed by Jens Axboe.

Overview

The NOOP scheduler inserts all incoming I/O requests into a simple FIFO queue and implements request merging.

The scheduler assumes I/O performance optimization will be handled at some other layer of the I/O hierarchy; e.g., at the block device; by an intelligent HBA such as a Serial Attached SCSI (SAS) RAID controller or by an externally attached controller such as a storage subsystem accessed through a switched Storage Area Network)^[1]

NOOP scheduler is best used with solid state devices such as flash memory or in general with devices that do not depend on mechanical movement to access data (meaning typical "hard disk" drive technology consisting of seek time primarily, plus rotational latency). Such non-mechanical devices do not require re-ordering of multiple I/O requests, a technique that groups together I/O requests that are physically close together on the disk, thereby reducing average seek time and the variability of I/O service time.^[2]

Other I/O schedulers

• CFQ
• Anticipatory scheduler
• Deadline scheduler

Notes and references

1. ^ "Choosing an I/O Scheduler for Red Hat Enterprise Linux 4 and the 2.6 Kernel". Red Hat. http://www.redhat.com/magazine/008jun05/features/schedulers/. Retrieved 2007-08-10. 
2. ^ "Switching IO Schedulers on runtime". http://www.linuxhowtos.org/System/iosched.htm. Retrieved 2007-08-10.