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
CMU-CS-02-177.ps
CMU-CS-02-177.pdf
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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