21-Queueing

21-Queueing - 1 Queuing Framework for Process Management...

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Unformatted text preview: 1 Queuing Framework for Process Management Evaluation Principles for Reasoning about Process Management/Scheduling Queuing Theory 2 Useful Facts From Queuing Theory W q = mean time a customer spends in the queue = arrival rate L q = W q number of customers in queue W = mean time a customer spends in the system L = W ( Little's theorem) number of customers in the system In words average length of queue is arrival rate times average waiting time 3 Process States Finite State Diagram 4 Queuing Models and Simulation Problem How do we size the ready queue, size any queue? decide how many jobs should be accepted? analyze scheduling algorithms? Decide how long we should wait for a job? Goals Simple arithmetic (back of envelope calculation) to calculate system behavior Basis for more complex analysis Approach to study systems too complex to produce simple mathematical model 5 CPU Scheduler Example Which is better: Round Robin or FIFO? How long does A take to go thru system? How big should be the ready queue? Mean, Mode, Variance? 6 Queuing Diagram for Processes Start Start Ready Queue Ready Queue Event Queue Event Queue Event Event Exit Exit Time Slice Time Slice CPU CPU 7 Queuing Diagram for Processes Start Start Ready Queue Ready Queue Event Queue Event Queue Event Event Exit Exit Time Slice Time Slice CPU CPU 8 Queuing Diagram for Processes Start Start Ready Queue Ready Queue Event Queue Event Queue Event Event Exit Exit Time Slice Time Slice CPU CPU 9 Queuing Diagram for Processes Start Start Ready Queue Ready Queue Event Queue Event Queue Event Event Exit Exit Time Slice Time Slice CPU CPU 10 Queuing Diagram for Processes Start Start Ready Queue Ready Queue Event Queue Event Queue Event Event Exit Exit Time Slice Time Slice CPU CPU 11...
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21-Queueing - 1 Queuing Framework for Process Management...

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