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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] |
Simplified Structure Of The Linux Kernel
Simplification, Simplify, or Simplified may refer to: Mathematics Simplification is the process of replacing a mathematical expression by an equivalent one, that is simpler (usually shorter), for example * Simplification of algebraic expressions, in computer algebra * Simplification of boolean expressions i.e. logic optimization * Simplification by conjunction elimination in inference in logic yields a simpler, but generally non-equivalent formula * Simplification of fractions Science * Approximations simplify a more detailed or difficult to use process or model Linguistics * Simplification of Chinese characters * Simplified English (other) * Text simplification Music * Simplified (band), a 2002 rock band from Charlotte, North Carolina * ''Simplified'' (album), a 2005 album by Simply Red * "Simplify", a 2008 song by Sanguine * "Simplify", a 2018 song by Young the Giant from ''Mirror Master'' See also * Muntzing (simplification of electric circuits) * Reduction (math ... [...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] |
FIFO (computing And Electronics)
Representation of a FIFO queue In computing and in systems theory, FIFO is an acronym for first in, first out (the first in is the first out), a method for organizing the manipulation of a data structure (often, specifically a data buffer) where the oldest (first) entry, or "head" of the queue, is processed first. Such processing is analogous to servicing people in a queue area on a first-come, first-served (FCFS) basis, i.e. in the same sequence in which they arrive at the queue's tail. FCFS is also the jargon term for the FIFO operating system scheduling algorithm, which gives every process central processing unit (CPU) time in the order in which it is demanded. FIFO's opposite is LIFO, last-in-first-out, where the youngest entry or "top of the stack" is processed first. A priority queue is neither FIFO or LIFO but may adopt similar behaviour temporarily or by default. Queueing theory encompasses these methods for processing data structures, as well as interactions between s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid-state Drives
A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is also sometimes called a semiconductor storage device, a solid-state device or a solid-state disk, even though SSDs lack the physical spinning disks and movable read–write heads used in hard disk drives (HDDs) and floppy disks. SSD also has rich internal parallelism for data processing. In comparison to hard disk drives and similar electromechanical media which use moving parts, SSDs are typically more resistant to physical shock, run silently, and have higher input/output rates and lower latency. SSDs store data in semiconductor cells. cells can contain between 1 and 4 bits of data. SSD storage devices vary in their properties according to the number of bits stored in each cell, with single-bit cells ("Single Level Cells" or "SLC") ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deadline Scheduler
The deadline scheduler is an I/O scheduler for the Linux kernel which was written in 2002 by Jens Axboe. Overview The main goal of the Deadline scheduler is to guarantee a start service time for a request. It does so by imposing a deadline on all I/O operations to prevent starvation of requests. It also maintains two deadline queues, in addition to the sorted queues (both read and write). Deadline queues are basically sorted by their deadline (the expiration time), while the sorted queues are sorted by the sector number. Before serving the next request, the deadline scheduler decides which queue to use. Read queues are given a higher priority, because processes usually block on read operations. Next, the deadline scheduler checks if the first request in the deadline queue has expired. Otherwise, the scheduler serves a batch of requests from the sorted queue. In both cases, the scheduler also serves a batch of requests following the chosen request in the sorted queue. By def ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ionice
nice is a program found on Unix and Unix-like operating systems such as Linux. It directly maps to a kernel call of the same name. nice is used to invoke a utility or shell script with a particular CPU priority, thus giving the process more or less CPU time than other processes. A niceness of -20 is the highest priority and 19 is the lowest priority. The default niceness for processes is inherited from its parent process and is usually 0. Etymology ''Niceness value'' is a number attached to processes in *nix systems, that is used along with other data (such as the amount of I/O done by each process) by the kernel process scheduler to calculate a process' 'true priority'which is used to decide how much CPU time is allocated to it. The program's name, nice, is an allusion to its task of modifying a process' niceness value. The term ''niceness'' itself originates from the idea that a process with a higher niceness value is ''nicer'' to other processes in the system and to users ... [...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] |
Kernel
Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learning * Kernelization, a technique for designing efficient algorithms ** Kernel, a routine that is executed in a vectorized loop, for example in general-purpose computing on graphics processing units *KERNAL, the Commodore operating system Mathematics Objects * Kernel (algebra), a general concept that includes: ** Kernel (linear algebra) or null space, a set of vectors mapped to the zero vector ** Kernel (category theory), a generalization of the kernel of a homomorphism ** Kernel (set theory), an equivalence relation: partition by image under a function ** Difference kernel, a binary equalizer: the kernel of the difference of two functions Functions * Kernel (geometry), the set of points within a polygon from which the whole polygon bound ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Red Hat
Red Hat, Inc. is an American software company that provides open source software products to enterprises. Founded in 1993, Red Hat has its corporate headquarters in Raleigh, North Carolina, with other offices worldwide. Red Hat has become associated to a large extent with its enterprise operating system Red Hat Enterprise Linux. With the acquisition of open-source enterprise middleware vendor JBoss, Red Hat also offers Red Hat Virtualization (RHV), an enterprise virtualization product. Red Hat provides storage, operating system platforms, middleware, applications, management products, and support, training, and consulting services. Red Hat creates, maintains, and contributes to many free software projects. It has acquired several proprietary software product codebases through corporate mergers and acquisitions and has released such software under open source licenses. , Red Hat is the second largest corporate contributor to the Linux kernel version 4.14 after Intel. On Octob ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rackspace
Rackspace Technology, Inc. is an American cloud computing company based in Windcrest, Texas, an inner suburb of San Antonio, Texas. The company also has offices in Blacksburg, Virginia, and Austin, Texas, as well as in Australia, Canada, United Kingdom, India, Dubai, Switzerland, the Netherlands, Germany, Singapore, Mexico, and Hong Kong. Its data centers are located in Amsterdam (Netherlands), Virginia (USA), Chicago (USA), Dallas (USA), London (UK), Frankfurt (Germany), Hong Hong (China), Kansas City (USA), New York City (USA), San Jose (USA), Shanghai (China), Queenstown (Singapore), and Sydney (Australia). History Although the founders began as application developers for end-users, they found that most companies did not either know how or want to host their applications. The founders wanted to focus on application development–not hosting–but they were unable to find an opportunity to outsource the hosting work. Eventually, the founders realized that it would be better ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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