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Reference · 2 min read

Interrupts and completed work

An interrupt is a notification that asks a processor to pay attention to an event. Hardware can use notifications to report completed transfers or other conditions instead of requiring software to constantly ask whether anything has changed.

How the pieces connect

The operating system connects notification mechanisms to routines that handle the event. Modern hardware often uses message-signaled interrupts rather than separate physical interrupt lines. Urgent work is kept short, with additional processing deferred as appropriate. Scheduling, processor affinity, and batching can influence the cost of handling a busy device.

An everyday example

A network controller may collect several packets before requesting attention, reducing the number of interruptions needed for a stream of traffic. An audio path has different timing priorities because buffers must be serviced regularly. Neither a larger nor a smaller raw count is automatically better; the useful interpretation depends on how much work each event represents.

Reading the information in context

Interrupt activity does not identify the root cause of every pause or audible interruption. It is one measurement among buffer timing, application load, and scheduling behavior. This conceptual explanation is not an instruction to change interrupt settings. Platform firmware and the relevant software package coordinate these mechanisms, and manual changes can have effects beyond the single device being inspected.

Reading map: Interrupts and completed workFirst 3 topics in reading order: How the pieces connect; An everyday example; Reading the information in context. Each topic links to its section or page.INSIDE THIS PAGEInterrupts and completed work1How the pieces connect1 paragraph2An everyday example1 paragraph3Reading the informationin context1 paragraph

Computer & System

Note these before you change anything

Useful facts to have to hand while reading about interrupts and completed work.

  • Motherboard or computer model and firmware version
  • Chipset driver package version
  • Any firmware settings changed from defaults
  • Unknown devices listed in Device Manager

Computer & System: One selected path: a device on a chipset bus

  1. Operating systemmanages devices
  2. Chipset driversidentify buses and power features
  3. ChipsetPCIe, USB and SATA links
  4. Firmware (UEFI)initialises hardware at start-up
  5. Attached deviceson those links
Conceptual schematic of a selected path, not every request. Shown in one direction; the reverse direction uses related layers. Real systems add services, filter drivers and firmware not shown. Highlighted: the layer a driver change affects.

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