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Completely Fair Queuing
Completely Fair Queuing (CFQ) 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. The length of the time slice and the number of requests a queue is allowed to submit depends on the I/O priority of the given process. Asynchronous requests for all processes are batched together in fewer queues, one per priority. While CFQ does not do explicit anticipatory I/O scheduling, it achieves the same effect of having good aggregate throughput for the system as a whole, by allowing a process queue to idle at the end of synchronous I/O thereby "anticipating" further close I/O from that process. It can be considered a natural extension of granting I/O time slices to a process. History Prior to the integration In February 2003 Andrea Arcangeli put forward his idea for a Stochastic Fa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
I/O Scheduling
Input/output (I/O) scheduling is the method that computer operating systems use to decide in which order I/O operations will be submitted to storage volumes. I/O scheduling is sometimes called disk scheduling. Purpose I/O scheduling usually has to work with hard disk drives that have long access times for requests placed far away from the current position of the disk head (this operation is called a seek). To minimize the effect this has on system performance, most I/O schedulers implement a variant of the elevator algorithm that reorders the incoming randomly ordered requests so the associated data would be accessed with minimal arm/head movement. I/O schedulers can have many purposes depending on the goals; common purposes include the following * To minimize time wasted by hard disk seeks * To prioritize a certain processes' I/O requests * To give a share of the disk bandwidth to each running process * To guarantee that certain requests will be issued before a particular ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux Kernel
The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU operating system, which was written to be a free (libre) replacement for Unix. Linux is provided under the GNU General Public License version 2 only, but it contains files under other compatible licenses. Since the late 1990s, it has been included as part of a large number of operating system distributions, many of which are commonly also called Linux. Linux is deployed on a wide variety of computing systems, such as embedded devices, mobile devices (including its use in the Android operating system), personal computers, servers, mainframes, and supercomputers. It can be tailored for specific architectures and for several usage scenarios using a family of simple commands (that is, without the need of manually editing its source code ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jens Axboe
Jens Axboe (born circa 1976) is a Linux kernel hacker. Work Axboe 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, io_uring and splice IO architecture. Jens is also the author of the blktrace utility and kernel parts, which provides a way to trace every block IO activity in the Linux kernel. blktrace exists in 2.6.17 and later Linux kernels. To facilitate his block layer work in the Linux kernel, Axboe created the flexible IO tester (fio) benchmarking and workload simulation tool. fio is able to simulate various types of I/O loads, such as synchronous, asynchronous, mmap, etc., as well as specifying the number of threads or processes, read vs. write mix, and various other parameters. fio was used to set the record in December 2012 for the highest number of I/Os-per-second (IOPS) in a single system. In May 2010 Axboe joined Fusion-io after leaving Oracle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Process (computing)
In computing, a process is the instance of a computer program that is being executed by one or many threads. There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions concurrently. While a computer program is a passive collection of instructions typically stored in a file on disk, a process is the execution of those instructions after being loaded from the disk into memory. Several processes may be associated with the same program; for example, opening up several instances of the same program often results in more than one process being executed. Multitasking is a method to allow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Queue (data Structure)
In computer science, a queue is a collection of entities that are maintained in a sequence and can be modified by the addition of entities at one end of the sequence and the removal of entities from the other end of the sequence. By convention, the end of the sequence at which elements are added is called the back, tail, or rear of the queue, and the end at which elements are removed is called the head or front of the queue, analogously to the words used when people line up to wait for goods or services. The operation of adding an element to the rear of the queue is known as ''enqueue'', and the operation of removing an element from the front is known as ''dequeue''. Other operations may also be allowed, often including a ''peek'' or ''front'' operation that returns the value of the next element to be dequeued without dequeuing it. The operations of a queue make it a first-in-first-out (FIFO) data structure. In a FIFO data structure, the first element added to the queue will b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Storage
Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is a device implementing such a storage mechanism. Notable types are the hard disk drive (HDD) containing a non-removable disk, the floppy disk drive (FDD) and its removable floppy disk, and various optical disc drives (ODD) and associated optical disc media. (The spelling ''disk'' and ''disc'' are used interchangeably except where trademarks preclude one usage, e.g. the Compact Disc logo. The choice of a particular form is frequently historical, as in IBM's usage of the ''disk'' form beginning in 1956 with the " IBM 350 disk storage unit".) Background Audio information was originally recorded by analog methods (see Sound recording and reproduction). Similarly the first video disc used an analog recording method. In the music indu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anticipatory Scheduling
Anticipatory scheduling is an algorithm for scheduling hard disk input/output (I/O scheduling). It seeks to increase the efficiency of disk utilization by "anticipating" future synchronous I/O, synchronous read operations. I/O scheduling "Deceptive idleness" is a situation where a process (computing), process appears to be finished reading from the disk when it is actually processing data in preparation of the next read operation. This will cause a normal Work-conserving scheduler, work-conserving I/O scheduler to switch to servicing I/O from an unrelated process. This situation is detrimental to the throughput of synchronous reads, as it degenerates into a seeking workload. Anticipatory scheduling overcomes deceptive idleness by pausing for a short time (a few milliseconds) after a read operation in ''anticipation'' of another close-by read requests. Anticipatory scheduling yields significant improvements in disk utilization for some workloads. In some situations the Apache web ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andrea Arcangeli
Andrea is a given name which is common worldwide for both males and females, cognate to Andreas, Andrej and Andrew. Origin of the name The name derives from the Greek word ἀνήρ (''anēr''), genitive ἀνδρός (''andrós''), that refers to man as opposed to woman (whereas ''man'' in the sense of ''human being'' is ἄνθρωπος, ''ánthropos''). The original male Greek name, ''Andréas'', represents the hypocoristic, with endearment functions, of male Greek names composed with the ''andr-'' prefix, like Androgeos (''man of the earth''), Androcles (''man of glory''), Andronikos (''man of victory''). In the year 2006, it was the third most popular name in Italy with 3.1% of newborns. It is one of the Italian male names ending in ''a'', with others being Elia (Elias), Enea (Aeneas), Luca ( Lucas), Mattia ( Matthias), Nicola ( Nicholas), Tobia (Tobias). In recent and past times it has also been used on occasion as a female name in Italy and in Spain, where it is c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Red Hat Enterprise Linux
Red Hat Enterprise Linux (RHEL) is a commercial open-source Linux distribution developed by Red Hat for the commercial market. Red Hat Enterprise Linux is released in server versions for x86-64, Power ISA, ARM64, and IBM Z and a desktop version for x86-64. Fedora Linux serves as its upstream source. All of Red Hat's official support and training, together with the Red Hat Certification Program, focuses on the Red Hat Enterprise Linux platform. The first version of Red Hat Enterprise Linux to bear the name originally came onto the market as "Red Hat Linux Advanced Server". In 2003, Red Hat rebranded Red Hat Linux Advanced Server to "Red Hat Enterprise Linux AS" and added two more variants, Red Hat Enterprise Linux ES and Red Hat Enterprise Linux WS. Red Hat uses strict trademark rules to restrict free re-distribution of their officially supported versions of Red Hat Enterprise Linux but still freely provides its source code. Third-party derivatives can be built and redistribut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sysfs
sysfs is a pseudo file system provided by the Linux kernel that exports information about various kernel subsystems, hardware devices, and associated device drivers from the kernel's device model to user space through virtual files. In addition to providing information about various devices and kernel subsystems, exported virtual files are also used for their configuration. sysfs provides functionality similar to the sysctl mechanism found in BSD operating systems, with the difference that sysfs is implemented as a virtual file system instead of being a purpose-built kernel mechanism, and that, in Linux, ''sysctl'' configuration parameters are made available at ''/proc/sys/'' as part of procfs, not sysfs which is mounted at ''/sys/''. History During the 2.5 development cycle, the Linux driver model was introduced to fix the following shortcomings of version 2.4: * No unified method of representing driver-device relationships existed. * There was no generic hotplug mechanism. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Budget Fair Queueing
Input/output (I/O) scheduling is the method that computer operating systems use to decide in which order I/O operations will be submitted to storage volumes. I/O scheduling is sometimes called disk scheduling. Purpose I/O scheduling usually has to work with hard disk drives that have long access times for requests placed far away from the current position of the disk head (this operation is called a seek). To minimize the effect this has on system performance, most I/O schedulers implement a variant of the elevator algorithm that reorders the incoming randomly ordered requests so the associated data would be accessed with minimal arm/head movement. I/O schedulers can have many purposes depending on the goals; common purposes include the following * To minimize time wasted by hard disk seeks * To prioritize a certain processes' I/O requests * To give a share of the disk bandwidth to each running process * To guarantee that certain requests will be issued before a particula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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. This scheduler is useful when it has been determined that the host should ''not'' attempt to re-order requests based on the sector numbers contained therein. In other words, the scheduler assumes that the host is unaware of how to productively re-order requests. There are (generally) three basic situations where this situation is desirable: * If I/O scheduling will be handled at a lower layer of the I/O stack. Examples of lower layers that might handle the scheduling include block devices, intelligent RAID controllers, Network Attached Storage, or an externally attached controller such as a storage subsystem accessed through a switched Storage Area Network. Since I/O requests are potentially rescheduled at the lower level, resequencing IOPs at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
