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Earliest Deadline First Scheduling
Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) the queue will be searched for the process closest to its deadline. This process is the next to be scheduled for execution. EDF is an ''optimal'' scheduling algorithm on preemptive uniprocessors, in the following sense: if a collection of independent ''jobs,'' each characterized by an arrival time, an execution requirement and a deadline, can be scheduled (by any algorithm) in a way that ensures all the jobs complete by their deadline, the EDF will schedule this collection of jobs so they all complete by their deadline. With scheduling periodic processes that have deadlines equal to their periods, EDF has a utilization bound of 100%. Thus, the schedulability test for EDF is: :U = \sum_^ \frac \leq 1, where the \left\ are the worst-case com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scheduling Algorithm
In computing, scheduling is the action of assigning resources to perform tasks. The resources may be processors, network links or expansion cards. The tasks may be threads, processes or data flows. The scheduling activity is carried out by a mechanism called a scheduler. Schedulers are often designed so as to keep all computer resources busy (as in load balancing), allow multiple users to share system resources effectively, or to achieve a target quality-of-service. Scheduling is fundamental to computation itself, and an intrinsic part of the execution model of a computer system; the concept of scheduling makes it possible to have computer multitasking with a single central processing unit (CPU). Goals A scheduler may aim at one or more goals, for example: * maximizing ''throughput'' (the total amount of work completed per time unit); * minimizing '' wait time'' (time from work becoming ready until the first point it begins execution); * minimizing '' latency'' or '' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OSEK
OSEK (''Offene Systeme und deren Schnittstellen für die Elektronik in Kraftfahrzeugen''; English: "''Open Systems and their Interfaces for the Electronics in Motor Vehicles''") is a standards body that has produced specifications for an embedded operating system, a communications stack, and a network management protocol for automotive embedded systems. It has produced related specifications, namely AUTOSAR. OSEK was designed to provide a reliable standard software architecture for the various electronic control units (ECUs) throughout a car. OSEK was founded in 1993 by a German automotive company consortium (BMW, Robert Bosch GmbH, DaimlerChrysler, Opel, Siemens, and Volkswagen Group) and the University of Karlsruhe. In 1994, the French cars manufacturers Renault and PSA Peugeot Citroën, which had a similar project called VDX (Vehicle Distributed eXecutive), joined the consortium. Therefore, the official name was OSEK/VDX and OSEK was registered trademark of Continental Automot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Processor Scheduling Algorithms
Processor may refer to: Computing Hardware * Processor (computing) ** Central processing unit (CPU), the hardware within a computer that executes a program *** Microprocessor, a central processing unit contained on a single integrated circuit (IC) **** Application-specific instruction set processor (ASIP), a component used in system-on-a-chip design **** Graphics processing unit (GPU), a processor designed for doing dedicated graphics-rendering computations **** Physics processing unit (PPU), a dedicated microprocessor designed to handle the calculations of physics **** Digital signal processor (DSP), a specialized microprocessor designed specifically for digital signal processing ***** Image processor, a specialized DSP used for image processing in digital cameras, mobile phones or other devices **** Neural processing unit (NPU), a class of specialized hardware accelerator or computer system designed to accelerate artificial intelligence and machine learning applications, inc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stack Resource Policy
The Stack Resource Policy (SRP) is a resource allocation policy used in real-time computing, used for accessing shared resources when using earliest deadline first scheduling Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) th .... It was defined by T. P. Baker. SRP is not the same as the Priority ceiling protocol which is for fixed priority tasks (FP). Function Each task is assigned a preemption level based upon the following formula where D(T_i) denotes the deadline of task i and \pi_i(T_i) denotes the preemption level of task i: D(T_i) \pi_i(T_j) Each resource R has a current ceiling C_R(V_R) that represents the maximum of the preemption levels of the tasks that may be blocked, when there are V units of R available and \mu_R(J) is the maximum units of R that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earliest Eligible Virtual Deadline First Scheduling
Earliest eligible virtual deadline first (EEVDF) is a dynamic priority proportional share scheduling algorithm for soft real-time systems. Algorithm EEVDF was first described in the 1995 paper "Earliest Eligible Virtual Deadline First : A Flexible and Accurate Mechanism for Proportional Share Resource Allocation" by Ion Stoica and Hussein Abdel-Wahab. It uses notions of virtual time, eligible time, virtual requests and virtual deadlines for determining scheduling priority. It has the property that when a job keeps requesting service, the amount of service obtained is always within the maximum quantum size of what it is entitled. Linux kernel scheduler In 2023, Peter Zijlstra proposed replacing the Completely Fair Scheduler (CFS) in the Linux kernel with an EEVDF process scheduler. The aim was to remove the need for CFS "latency nice" patches. The EEVDF scheduler replaced CFS in version 6.6 of the Linux kernel. See also * Brain Fuck Scheduler * Earliest deadline first schedu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Priority Scheduling
Dynamic priority scheduling is a type of scheduling algorithm in which the priorities are calculated during the execution of the system. The goal of dynamic priority scheduling is to adapt to dynamically changing progress and to form an optimal configuration in a self-sustained manner. It can be very hard to produce well-defined policies to achieve the goal depending on the difficulty of a given problem. Earliest deadline first scheduling and Least slack time scheduling are examples of Dynamic priority scheduling algorithms. Optimal schedulable utilization The idea of real-time scheduling is to confine processor utilization under schedulable utilization of a certain scheduling algorithm, which is scaled from 0 to 1. Higher schedulable utilization means higher utilization of resource and the better the algorithm. In preemptible scheduling, dynamic priority scheduling such as earliest deadline first (EDF) provides the optimal schedulable utilization of 1 in contrast to less than 0 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hierarchical Scheduler
A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important concept in a wide variety of fields, such as architecture, philosophy, design, mathematics, computer science, organizational theory, systems theory, systematic biology, and the social sciences (especially political science). A hierarchy can link entities either directly or indirectly, and either vertically or diagonally. The only direct links in a hierarchy, insofar as they are hierarchical, are to one's immediate superior or to one of one's subordinates, although a system that is largely hierarchical can also incorporate alternative hierarchies. Hierarchical links can extend "vertically" upwards or downwards via multiple links in the same direction, following a path. All parts of the hierarchy that are not linked vertically to one anothe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Temporal Isolation Among Virtual Machines
Temporal isolation or performance isolation among virtual machine (VMs) refers to the capability of isolating the temporal behavior (or limiting the temporal interferences) of multiple VMs among each other, despite them running on the same physical host and sharing a set of physical resources such as processors, memory, and disks. Introduction to the problem One of the key advantages of using virtualization in server consolidation, is the possibility to seamlessly "pack" multiple under-utilized systems into a single physical host, thus achieving a better overall utilization of the available hardware resources. In fact, an entire operating system (OS), along with the applications running within, can be run in a virtual machine (VM). However, when multiple VMs concurrently run on the same physical host, they share the available physical resources, including CPU(s), network adapter(s), disk(s) and memory. This adds a level of unpredictability in the performance that may be exhibit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kernel-based Virtual Machine
Kernel-based Virtual Machine (KVM) is a free and open-source virtualization module in the Linux kernel that allows the Kernel (operating system), kernel to function as a hypervisor. It was merged into the Mainline Linux, mainline Linux kernel in version 2.6.20, which was released on February 5, 2007. KVM requires a processor with hardware virtualization extensions, such as Intel VT or AMD-V. KVM has also been ported to other operating systems such as FreeBSD and illumos in the form of loadable kernel modules. KVM was originally designed for x86 processors but has since been porting, ported to IBM ESA/390, ESA/390, PowerPC, IA-64, and ARM architecture, ARM. The IA-64 port was removed in 2014. KVM supports hardware-assisted virtualization for a wide variety of guest operating systems including BSD, Solaris (operating system), Solaris, Microsoft Windows, Windows, Haiku (operating system), Haiku, ReactOS, Plan 9 from Bell Labs, Plan 9, AROS Research Operating System, AROS, macOS, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual Machine
In computing, a virtual machine (VM) is the virtualization or emulator, emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination of the two. Virtual machines differ and are organized by their function, shown here: * ''System virtual machines'' (also called full virtualization VMs, or SysVMs) provide a substitute for a real machine. They provide the functionality needed to execute entire operating systems. A hypervisor uses native code, native execution to share and manage hardware, allowing for multiple environments that are isolated from one another yet exist on the same physical machine. Modern hypervisors use hardware-assisted virtualization, with virtualization-specific hardware features on the host CPUs providing assistance to hypervisors. * ''Process virtual machines'' are designed to execute computer programs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCHED DEADLINE
SCHED_DEADLINE is a CPU scheduling (computing), scheduler available in the Linux kernel since version 3.14, Linux Weekly News, Deadline scheduling for Linux OSNews, Deadline Scheduling in the Linux Kernel based on the earliest deadline first (EDF) and constant bandwidth server (CBS) L. Abeni and G. Buttazzo, "Integrating multimedia applications in hard real-time systems," Proc. of the 19th IEEE Real-Time Systems Symposium, Madrid, 1998, pp.4-13 algorithms, supporting resource reservations: each task scheduled under such policy is associated with a ''budg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux Kernel
The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the kernel for the GNU operating system (OS) which was created to be a free software, free replacement for Unix. Since the late 1990s, it has been included in many Linux distributions, operating system distributions, many of which are called Linux. One such Linux kernel operating system is Android (operating system), Android which is used in many mobile and embedded devices. Most of the kernel code is written in C (programming language), C as supported by the GNU compiler collection (GCC) which has extensions beyond standard C. The code also contains assembly language, assembly code for architecture-specific logic such as optimizing memory use and task execution. The kernel has a Modular programming, modular design such that modules can be inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
