Interrupt coalescing, also known as interrupt moderation, is a technique in which events which would normally trigger a
hardware interrupt
In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, ...
are held back, either until a certain amount of work is pending, or a
timeout
Time-out, Time Out, or timeout may refer to:
Time
* Time-out (sport), in various sports, a break in play, called by a team
* Television timeout, a break in sporting action so that a commercial break may be taken
* Timeout (computing), an enginee ...
timer triggers. Used correctly, this technique can reduce interrupt load by up to an order of magnitude, while only incurring relatively small latency penalties. Interrupt coalescing is typically combined with either a hardware FIFO or
direct memory access
Direct memory access (DMA) is a feature of computer systems and allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU).
Without DMA, when the CPU is using programmed input/output, it is t ...
, to allow for continued data throughput while interrupts are being held back.
Interrupt coalescing is a common feature of modern network cards, but the technique dates back to early computer
UART
A universal asynchronous receiver-transmitter (UART ) is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significan ...
s such as the
16550 UART chip used in the
IBM PC
The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...
's serial interface, at a time when even servicing the interrupt rates required by the low data rate serial data streams of the day was taxing for contemporary CPUs.
Interrupt coalescing can also be implemented without support in hardware, by disabling interrupts in the interrupt controller and using timer-based
polling
Poll, polled, or polling may refer to:
Figurative head counts
* Poll, a formal election
** Election verification exit poll, a survey taken to verify election counts
** Polling, voting to make decisions or determine opinions
** Polling places o ...
.
See also
*
I/O processor
In computing, channel I/O is a high-performance input/output (I/O) architecture that is implemented in various forms on a number of computer architectures, especially on mainframe computers. In the past, channels were generally implemented with cu ...
*
Timer coalescing
Timer coalescing is a computer system energy-saving technique that reduces central processing unit (CPU) power consumption by reducing the precision of software timers used for synchronization of process wake-ups, minimizing the number of times th ...
References
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Interrupts