CSC 7103 Final Study Guide

CSC 7103 Final Study Guide - CSC 7103 Page 1 of 12 Final...

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CSC 7103 12/1/2009 Page 1 of 12 Final review Chapter 5 Precedence and communication process models are interacting process models because they show the cost/communication of processes/processors in a system Turnaround time is defined as the sum of service and queueing times due to waiting for other processes. Speedup can occur when a task is partitioned into multiple processes for execution. The makespan is the total completion time of a set of interacting processes. The unified speedup model integrated three major components, algorithm development, system architecture, and scheduling policy with the objective of minimizing the makespan of a set of processes. Static workload distribution is referred to as load sharing , and dynamic workload distribution is called load balancing . Static Scheduling Kendall’s notation: X/Y/C : X => an arrival process X, a service time distribution of Y, and c servers. M is for a Markovian distribution, and generally a processor pool model can be modeled as an M/M/k queue. Isolated workstation and processor pool models do not allow task migration, but the migration workstation model does. Isolated workstation is generally M/M/1. Scheduling to optimize the makespan is NP-complete except for some restricted cases. We only studied the precedence process model. In the precedence process model, the critical path is the longest execution path in the DAG, which is the lower bound of the makespan. The precedence process model includes LS, ELS, and ETF scheduling. Figures 5.5 and 5.6 illustrate these scheduling algorithms. Dynamic Scheduling The Goal of dynamic scheduling is to load share and balance dynamically. This goal is achieved by migrating tasks from heavily loaded processors to lightly loaded processors. Two types of task migration algorithms: Sender-initiated Transfer policy (when to transfer?) Selection policy (which task to transfer?) Location policy (where to transfer?) Potentially unstable. Receiver-initiated
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CSC 7103 12/1/2009 Page 2 of 12 Real-time Scheduling A real-time task consists of S i , the earliest start time, D i , the deadline to finish the task and C i , the worst-case completion time. A set of real-time tasks is called a real-time task set or a real-time system . A system of real-time tasks is called hard real-time system if all of the tasks in the system must complete execution within their respective deadlines. Even if one task misses its deadline, the whole system is considered incorrectly executed. A system of real-time tasks is called soft real-time system if the performance is judged by how many tasks missed deadline and by how much. A schedule for a real-time system is a CPU assignment to the tasks of the system such that a CPU is assigned to no more than one task at one time.
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