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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 c ... [...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 process called 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' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fixed-priority Pre-emptive Scheduling
Fixed-priority preemptive scheduling is a scheduling system commonly used in real-time systems. With fixed priority preemptive scheduling, the scheduler ensures that at any given time, the processor executes the highest priority task of all those tasks that are currently ready to execute. The preemptive scheduler has a clock interrupt task that can provide the scheduler with options to switch after the task has had a given period to execute—the time slice. This scheduling system has the advantage of making sure no task hogs the processor for any time longer than the time slice. However, this scheduling scheme is vulnerable to process or thread lockout: since priority is given to higher-priority tasks, the lower-priority tasks could wait an indefinite amount of time. One common method of arbitrating this situation is aging, which gradually increments the priority of waiting processes and threads, ensuring that they will all eventually execute. Most real-time operating systems ... [...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 **** Coprocessor **** Floating-point unit **** Network processor, a microprocessor specifically targeted at the networking application domain ** Multi-core processor, single component ... [...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. It was defined by T. P. Baker. SRP is not the same as the Priority ceiling protocol In real-time computing, the priority ceiling protocol is a synchronization protocol for shared resources to avoid unbounded priority inversion and mutual deadlock due to wrong nesting of critical sections. In this protocol each resource is assign ... 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] |
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 0.6 ... [...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 philosophy). 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 a ... [...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 exhibite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kernel-based Virtual Machine
Kernel-based Virtual Machine (KVM) is a virtualization module in the Linux kernel that allows the kernel to function as a hypervisor. It was merged into the 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 ported to S/390, PowerPC, IA-64, and ARM. KVM provides hardware-assisted virtualization for a wide variety of guest operating systems including Linux, BSD, Solaris, Windows, Haiku, ReactOS, Plan 9, AROS Research Operating System and macOS. In addition, Android 2.2, GNU/Hurd ( Debian K16), Minix 3.1.2a, Solaris 10 U3 and Darwin 8.0.1, together with other operating systems and some newer versions of these listed, are known to work with certain limitatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual Machine
In computing, a virtual machine (VM) is the virtualization/ emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination. Virtual machines differ and are organized by their function, shown here: * '' System virtual machines'' (also termed full virtualization VMs) provide a substitute for a real machine. They provide functionality needed to execute entire operating systems. A hypervisor uses native execution to share and manage hardware, allowing for multiple environments which are isolated from one another, yet exist on the same physical machine. Modern hypervisors use hardware-assisted virtualization, virtualization-specific hardware, primarily from the host CPUs. * Process virtual machines are designed to execute computer programs in a platform-independent environment. Some virtual machine emulators, such as QEMU a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCHED DEADLINE
SCHED_DEADLINE is a CPU 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 scheduling, Earliest Deadline First (EDF) and Constant Bandwidth Server (CBS) L. Abeni and G. Buttazzo, "Integrating multimedia applications in hard real-t ... [...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 c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AQuoSA
AQuoSA (Adaptive Quality of Service Architecture) is an open architecture for the provisioning of adaptive Quality of Service functionality into the Linux kernel. The project features a flexible, portable, lightweight and open architecture for supporting QoS related services on the top of a general-purpose operating system as Linux. The architecture is well founded on formal scheduling analysis and control theoretical results. A key feature of AQuoSA is the Resource Reservation layer that is capable of dynamically adapting the CPU allocation for QoS aware applications based on their run-time requirements. In order to provide such functionality, AQuoSA embeds a kernel-level CPU scheduler implementing a resource reservation mechanism for the CPU based on Earliest Deadline First (EDF). This gives the ability to the Linux kernel to realize (partially) temporal isolation among the tasks running within the system. AQuoSA is one of a few projects that provides real-time scheduling c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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