See also
- Deadline scheduler
- Noop scheduler
- CFQ scheduler
- Native Command Queuing (NCQ)
- Scheduling (computing)
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 read operations.
"Deceptive idleness" is a situation where a 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 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. [1] 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. [2]
Anticipatory scheduling yields significant improvements in disk utilization for some workloads. [3] In some situations the Apache web server may achieve up to 71% more throughput from using anticipatory scheduling. [4]
The Linux anticipatory scheduler may reduce performance on disks using Tagged Command Queuing (TCQ), high performance disks, and hardware RAID arrays. [5] An anticipatory scheduler (AS) was the default Linux kernel scheduler between 2.6.0 and 2.6.18, by which time it was replaced by the CFQ scheduler.
As of kernel version 2.6.33, the Anticipatory scheduler has been removed from the Linux kernel. [6] The reason being that while useful, the scheduler's effects could be achieved through tuned use of other schedulers (mostly CFQ, which can also be configured to idle with the slice_idle tunable). [7] Since the anticipatory scheduler added maintenance overhead while not improving the workload coverage of the Linux kernel, it was deemed redundant.
In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point. This allows multiple processes to share a single central processing unit (CPU), and is an essential feature of a multitasking operating system.
In UNIX computing, the system load is a measure of the amount of computational work that a computer system performs. The load average represents the average system load over a period of time. It conventionally appears in the form of three numbers which represent the system load during the last one-, five-, and fifteen-minute periods.
In computing, scheduling is the method by which work is assigned to resources that complete the work. The work may be virtual computation elements such as threads, processes or data flows, which are in turn scheduled onto hardware resources such as processors, network links or expansion cards.
In computer operating systems, paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storage in same-size blocks called pages. Paging is an important part of virtual memory implementations in modern operating systems, using secondary storage to let programs exceed the size of available physical memory.
In computer data storage, data striping is the technique of segmenting logically sequential data, such as a file, so that consecutive segments are stored on different physical storage devices.
TimesTen is an in-memory, relational database management system with persistence and recoverability. Originally designed and implemented at Hewlett-Packard labs in Palo Alto, California, TimesTen spun out into a separate startup in 1996 and was acquired by Oracle Corporation in 2005.
Completely Fair Queuing (CFQ) is an I/O scheduler for the Linux kernel which was written in 2003 by Jens Axboe.
In computer science, asynchronous I/O is a form of input/output processing that permits other processing to continue before the transmission has finished.
OS-level virtualization is an operating system paradigm in which the kernel allows the existence of multiple isolated user space instances. Such instances, called containers, Zones, virtual private servers (OpenVZ), partitions, virtual environments (VEs), virtual kernels, or jails, may look like real computers from the point of view of programs running in them. A computer program running on an ordinary operating system can see all resources of that computer. However, programs running inside of a container can only see the container's contents and devices assigned to the container.
OpenVZ is an operating-system-level virtualization technology for Linux. It allows a physical server to run multiple isolated operating system instances, called containers, virtual private servers (VPSs), or virtual environments (VEs). OpenVZ is similar to Solaris Containers and LXC.
Jens Axboe is a Linux kernel hacker.
Input/output (I/O) scheduling is the method that computer operating systems use to decide in which order the block I/O operations will be submitted to storage volumes. I/O scheduling is sometimes called disk scheduling.
Linux startup process is the multi-stage initialization process performed during booting a Linux installation. It is in many ways similar to the BSD and other Unix-style boot processes, from which it derives.
The Completely Fair Scheduler (CFS) is a process scheduler which was merged into the 2.6.23 release of the Linux kernel and is the default scheduler. It handles CPU resource allocation for executing processes, and aims to maximize overall CPU utilization while also maximizing interactive performance.
The NOOP scheduler is the simplest I/O scheduler for the Linux kernel. This scheduler was developed by Jens Axboe.
The deadline scheduler is an I/O scheduler for the Linux kernel which was written in 2002 by Jens Axboe.
A process is a program in execution. An integral part of any modern-day operating system (OS). The OS must allocate resources to processes, enable processes to share and exchange information, protect the resources of each process from other processes and enable synchronization among processes. To meet these requirements, the OS must maintain a data structure for each process, which describes the state and resource ownership of that process, and which enables the OS to exert control over each process.
The Brain Fuck Scheduler (BFS) is a process scheduler designed for the Linux kernel in August 2009 as an alternative to the Completely Fair Scheduler (CFS) and the O(1) scheduler. BFS was created by veteran kernel programmer Con Kolivas.
cgroups is a Linux kernel feature that limits, accounts for, and isolates the resource usage of a collection of processes.
dm-cache is a component of the Linux kernel's device mapper, which is a framework for mapping block devices onto higher-level virtual block devices. It allows one or more fast storage devices, such as flash-based solid-state drives (SSDs), to act as a cache for one or more slower storage devices such as hard disk drives (HDDs); this effectively creates hybrid volumes and provides secondary storage performance improvements.
|journal= (help)