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Comment: Re:Surprised? (Score 5, Informative) 292

by jrschulz (#18832235) Attached to: The Completely Fair Scheduler
A scheduler is the piece of software that brings you the illusion of multi-tasking. Because a single processor (with a single core) can only run one process at the same time, the operating system switches the process currently running. And it does this very fast (IIRC up to 1000 times a second in the case of linux).

The scheduler decides which process runs when and has to make sure that no process has to wait in the queue forever without getting his share of CPU time (this is what is called "starving").

Since the scheduler is a program by itself, it has a specific runtime characteristic, usually dependent of the number of programs waiting for their CPU share. The special property of the current scheduler in linux is that its runtime is in fact independent of this number. That's expressed in CS by O(1).

Utility is when you have one telephone, luxury is when you have two, opulence is when you have three -- and paradise is when you have none. -- Doug Larson