Computer Science Department
School of Computer Science, Carnegie Mellon University


A Note on Comparing Response Times in the
M/GI/1/FB and M/GI/1/PS Queues

Adam Wierman, Nikhil Bansal, Mor Harchol-Balter

September 2002

Keywords: Scheduling; M/G/1; FB; LAS; SET; feedback, least attained service, shortest elapsed time, PS, processor sharing, sojourn time, response time

Two widely used scheduling policies used in the absence of knowledge of job sizes are Processor Sharing (PS) and Feedback (FB). While a lot of work has been done on comparing their performance on particular job size distributions, a general comparison has not been done. We compare the overall mean response time (a.k.a. sojourn time) of the PS and FB queues under an M/GI/1 system. We show that FB outperforms PS when the service distribution has a decreasing failure rate; but that when the failure rate of the service distribution is increasing, PS outperforms FB. This answers a question posed by Coffman and Denning.

7 pages

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