Noop scheduler
Encyclopedia
The NOOP scheduler is the simplest I/O scheduler
for the Linux kernel
. This scheduler was developed by Jens Axboe
.
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)
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.
I/O scheduling
Input/output scheduling is a term used to describe the method computer operating systems decide the order that block I/O operations will be submitted to storage volumes...
for the Linux kernel
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
. This scheduler was developed by Jens Axboe
Jens Axboe
Jens Axboe is a Linux kernel hacker. He is the current Linux kernel maintainer of the block layer and other block devices, along with contributing the CFQ I/O scheduler, Noop scheduler, Deadline scheduler and splice IO architecture. Jens is also the author of the blktrace utility and kernel parts,...
.
Overview
The NOOP scheduler inserts all incoming I/O requests into a simple FIFOFIFO
FIFO is an acronym for First In, First Out, an abstraction related to ways of organizing and manipulation of data relative to time and prioritization...
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)
NOOP scheduler is best used with solid state devices such as flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
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.
Other I/O schedulers
- CFQCFQCompletely Fair Queuing is an I/O scheduler for the Linux kernel which was written in 2003 by Jens Axboe.-Description:CFQ places synchronous requests submitted by processes into a number of per-process queues and then allocates timeslices for each of the queues to access the disk...
- Anticipatory schedulerAnticipatory schedulingAnticipatory scheduling is an algorithm for scheduling hard disk input/output. It seeks to increase the efficiency of disk utilization by "anticipating" synchronous read operations....
- Deadline schedulerDeadline schedulerDeadline scheduler is an I/O scheduler for the Linux kernel which was written in 2002 by Jens Axboe.- Overview :The goal of the Deadline scheduler is to guarantee a start service time for a request. It does that by imposing a deadline on all I/O operations to prevent starvation of requests. It also...