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Hiệu suất của hệ thống thông tin máy tính P6

IN this chapter we continue the study of MlGjl q ueueing models. In particular, we will study the influence of various new scheduling disciplines, in comparison to the FCFS scheduling we have addressed in Chapter 5. We address non-preemptive priority scheduling in Section 6.1 and preemptive priority scheduling in Section 6.2. A limiting case of the non-preemptive priority scheduling is shortest job next scheduling, which is discussed in Section 6.3. | Performance of Computer Communication Systems A Model-Based Approach. Boudewijn R. Haverkort Copyright 1998 John Wiley Sons Ltd ISBNs 0-471-97228-2 Hardback 0-470-84192-3 Electronic Chapter 6 M G 1 queueing models with various scheduling disciplines IN this chapter we continue the study of M G 1 queueing models. In particular we will study the influence of various new scheduling disciplines in comparison to the FCFS scheduling we have addressed in Chapter 5. We address non-preemptive priority scheduling in Section 6.1 and preemptive priority scheduling in Section 6.2. A limiting case of the non-preemptive priority scheduling is shortest job next scheduling which is discussed in Section 6.3. Then in Section 6.4 we discuss the round robin scheduling strategy and in Section 6.5 its limiting case processor sharing scheduling. Finally we discuss scheduling disciplines based on the already elapsed service time of jobs in Section 6.6. 6.1 Non-preemptive priority scheduling Up till now we have assumed that all the jobs that need to be served have the same priority. In practice this is often not the case. In communication systems as an example short packets that contain control information might have priority over the generally longer user packets. Another case where priorities are needed is in integrated services communication systems which transmit real-time data such as voice or video samples next to time-insensitive data. Also in computer system scheduling multiple priority classes do make sense e.g. to distinguish between interactive jobs and computation-intensive batch jobs. To illustrate the need for priority scheduling let us consider the following example. Example 6.1. A computer center without priorities. Consider a computer center where jobs enter as a Poisson process with rate A. Of the 116 6 M G 1 queueing models with various scheduling disciplines a P e w 1 0.1540 0.0222 2 0.3080 0.0542 3 0.4620 0.1046 4 0.6160 0.1953 5 0.7700 0.4076 6 0.9240 1.4803 Table 6.1