|CS 321 Spring 2013 > Lecture Notes for Wednesday, February 20, 2013|
Actual scheduling algorithms are endlessly tweaked. Here are some of the major ideas used. An important idea is the quantum: the maximum amount of time a process is allowed to run before it is preempted. Making this too short leads to too much time spent doing context switches. Making it too long leads to poor response times. Note that a process can run for less time, if it blocks or terminates (or, in some systems, if it voluntarily relinquishes the processor).
Real-time scheduling is much simpler, but much less versatile. It makes strong guarantees; sometimes this is impossible. A set of processes and guarantees is schedulable is the processes can be scheduled in such a way that the guarantees are met.