Modern Operating System by Andrew S. Tanenbaum

Author:Andrew S. Tanenbaum
Language: eng
Format: mobi
Tags: ISBN 0-13-031358-0, 976 pages
Publisher: Prentice Hall PTR
Published: 0101-01-01T00:00:00+00:00

then RMS is guaranteed to work. For 3, 4, 5, 10, 20, and 100, the maximum permitted utilizations are 0.780, 0.757, 0.743, 0.718, 0.705, and 0.696. As m → ∞, the maximum utilization is asymptotic to ln 2. In other words. Liu and Layland proved that for three processes, RMS always works if the CPU utilization is at or below 0.780. In our first example, it was 0.808 and RMS worked, but we were just lucky. With different periods and run times, a utilization of 0.808 might fail. In the second example, the CPU utilization was so high (0.975), there was no hope that RMS could work.

In contrast, EDF always works for any schedulable set of processes. It can achieve 100% CPU utilization. The price paid is a more complex algorithm. Thus in an actual video server if the CPU utilization is below the RMS limit, RMS can be used. Otherwise EDF should be chosen.

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