CODEWITHSUNDEEP
operating-systemkernel
Physician
Physician

Reputation: 483

Are i/o device polling intervals often consistent?

this is a quick question about common existing operating systems.

Is a polled io device (say of 120hz or 250hz) generally getting polled at a fixed rate or there are usually considerable fluctuations in polling intervals, and if there are fluctuations, are they in terms of milliseconds or micro/nanoseconds?

Upvotes: 0

Views: 86

Answers (1)

Frank Hoeflich
Frank Hoeflich

Reputation: 650

This depends upon the processor architecture, system and application design. Your basic reference is this Wikipedia article.

In an embedded system where the result and latency of polling a particular device may be the most important and central purpose of the system, you are likely to see a tight loop busy-waiting at processor instruction speeds (micro/nanoseconds) with low jitter. These intervals may not be completely deterministic due to modern processor architecture improvements such as speculative branching depending on the surrounding code; see this relevant StackOverflow answer.

In a multitasking system doing lots of things and occasionally polling for, say, keystrokes from a HID of course there will be considerably higher latency in units more like milliseconds. Tasks may switch, processes may be swapped in and out etc.

This is a quick answer to your quick question - trying to put you into the ballpark but making clear that there could be a lot at play here depending on your environment.

Upvotes: 1

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