Timer coalescing is a computer system
energy-saving
Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively (using less energy for continuous service) or changing one's behavior to use less service (f ...
technique that reduces
central processing unit
A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
(CPU) power consumption by reducing the precision of
software timer
A timer is a specialized type of clock used for measuring specific time intervals.
Timers can be categorized into two main types.
The word "timer" is usually reserved for devices that counts down from a specified time interval, while devices th ...
s used for synchronization of process wake-ups, minimizing the number of times the CPU is forced to perform the relatively power-costly operation of entering and exiting
idle states.
[
]
Implementations of timer coalescing
*The 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 ope ...
gained support for deferrable timers in 2.6.22,[ and controllable "timer slack" for threads in 2.6.28 allowing timer coalescing.]Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
from Windows 7
Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on July 22, 2009, and became generally available on October 22, 2009. It is the successor to Windows Vista, released nearly ...
onward.
*Apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
's XNU
XNU is the computer operating system (OS) kernel developed at Apple Inc. since December 1996 for use in the Mac OS X (now macOS) operating system and released as free and open-source software as part of the Darwin OS, which in addition to macOS ...
kernel based OS X
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
gained support as of OS X Mavericks
OS X Mavericks (version 10.9) is the 10th major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers. OS X Mavericks was announced on June 10, 2013, at WWDC 2013, and was released on October 22, 2013, worl ...
.FreeBSD
FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
supports it since September 2010.
See also
* Advanced Configuration and Power Interface
Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto c ...
(ACPI)
* Advanced Programmable Interrupt Controller
In computing, Intel's Advanced Programmable Interrupt Controller (APIC) is a family of interrupt controllers. As its name suggests, the APIC is more advanced than Intel's 8259 Programmable Interrupt Controller (PIC), particularly enabling the co ...
(APIC)
* High Precision Event Timer
The High Precision Event Timer (HPET) is a hardware timer available in modern x86-compatible personal computers. Compared to older types of timers available in the x86 architecture, HPET allows more efficient processing of highly timing-sensitiv ...
(HPET)
* HLT (x86 instruction)
In the x86 computer architecture, HLT (halt) is an assembly language instruction which halts the central processing unit (CPU) until the next external interrupt is fired. Interrupts are signals sent by hardware devices to the CPU alerting it that ...
* Interrupt coalescing
Interrupt coalescing, also known as interrupt moderation, is a technique in which events which would normally trigger a hardware interrupt are held back, either until a certain amount of work is pending, or a timeout timer triggers. Used correct ...
* Programmable interval timer
In computing and in embedded systems, a programmable interval timer (PIT) is a counter that generates an output signal when it reaches a programmed count. The output signal may trigger an interrupt.
Common features
PITs may be one-shot or periodic ...
* Time Stamp Counter
The Time Stamp Counter (TSC) is a 64-bit register present on all x86 processors since the Pentium. It counts the number of CPU cycles since its reset. The instruction RDTSC returns the TSC in EDX:EAX. In x86-64 mode, RDTSC also clears the upper 3 ...
(TSC)
References
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Operating system kernels
Synchronization