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Unformatted text preview: cess B). Thus, there is kernel activity during each transition from one process to another. At other times, kernel activity can occur without switching processes, such as when a page fault can be satisﬁed by using a page that is already in memory. 9.1.2 Time from an Application Program’s Perspective
From the perspective of an application program, the ﬂow of time can be viewed as alternating between periods when the program is active (executing its instructions), and inactive (waiting to be scheduled by the operating system). It only performs useful computation when its process is operating in user mode. Figure 9.2(b) illustrates how program A would view the ﬂow of time. It is active during the light-colored regions, when process A is executing in user mode; otherwise it is inactive. As a way to quantify the alternations between active and inactive time periods, we wrote a program that continuously monitors itself and determines when there have been long periods of inactivity. It then generates a trace showing the alternations between periods of activity and...
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- Spring '10
- The American