Package nl.tudelft.simulation.examples.dsol.timesharedcomputer
The next example illustrates a time-shared computer facility considered by Adiri and Avi-Itzhak(1969). A company has a computer system consisting of a single central processing unit (CPU) and n terminals. The operator of each terminal "thinks" for an amount of time that is an exponential random variable with a mean of 25seconds and then sends to the CPU a job having service time distributed exponentially with mean=0.8seconds. Arriving jobs join a single queue for the CPU but are served in a round-robin rather than FIFO manner. That is, the CPU allocates to each jobs a maximum service quantum of length q=0.1 second. If the remaining service time of a job (s) is no more than q, the CPU spends s seconds plus a fixed swap time x=0.015 second, processing the job, which then returns to its terminal. However, if s>q. the CPU spends q+x second processing the job, which then joins the end of the queue, and its remaining service time is decremented by q seconds. This process is repeated until the job's service is eventually completed at which point it returns to its terminal, whose operator begins another think time.
We simulate this system for 1000 job completions. and estimate the expected average response times of these jobs, the expected time-average number of jobs waiting in queue and the expected utilization of the CPU. All terminals are in the think state at t=0. The company would like to know how many terminals it can have on its system and still provide users with an average response time of no more than 30 seconds.
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- Author:
- Peter Jacobs, Alexander Verbraeck
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ClassesClassDescriptionThe Computer example as published in Simulation Modeling and Analysis by A.M.A counter which stops after a predifined number of jobs.The CPU example as published in Simulation Modeling and Analysis by A.M.The Computer job as published in Simulation Modeling and Analysis by A.M.The Terminal as published in Simulation Modeling and Analysis by A.M.