Page "Asynchronous I/O" Paragraph 33

That, in fact, is the problem with using polling in any form to synthesize a different form of asynchronous I / O.

Every CPU cycle that is a poll is wasted, and lost to overhead rather than accomplishing a desired task.

Every CPU cycle that is not a poll represents an increase in latency of reaction to pending I / O.

Striking an acceptable balance between these two opposing forces is difficult.

( This is why hardware interrupt systems were invented in the first place.