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Tutorials Program - SIGMETRICS 2001 / Performance 2001

Performance Tradeoffs in Priority Scheduling

Jeffrey P. Buzen <>

Consulting Scientist
BMC Software
880 Winter St.
Waltham, MA 02454

Priority scheduling always involves tradeoffs - high priority customers do better, while low priority customers do worse. The equations that characterize these tradeoffs can be found in advanced texts on queuing theory. However, because these equations are so complex, it is difficult to gain an appreciation of the critical underlying issues simply by examining the corresponding closed form analytic solutions.

This tutorial presents an intuitive, easy to understand explanation of the basic factors that regulate performance in systems with priority scheduling. The emphasis is on intuition and insight rather than mathematical details. Nevertheless, the tutorial will provide enough information to enable attendees to carry out "back of the envelope" computations and develop simple programs for analyzing specific problems in priority scheduling.

The basis for this tutorial is provided by Kleinrock's well known conservation laws for priority systems. Several variants of these laws will be considered. In addition, the implications of achievability constraints and the transparency principle will be examined from both an analytic and a geometric perspective.

A series of numerical examples and sample applications will be used to illustrate the main points. The first involves "class of service/quality of service" scheduling in Web server farms. The second involves the goal oriented dispatcher (Workload Manager) developed by IBM for their largest mainframe systems. In addition to providing concrete examples of the necessary computational procedures, the applications also incorporate unexpected and counter-intuitive results.

Who should attend?
Anyone interested in learning more about the performance of priority based systems. No prior knowledge of specific results from queuing theory will be required, but basic familiarity with performance concepts and algebraic computations will be assumed. This tutorial should be of interest to practitioners responsible for the management of system performance, educators seeking classroom material on this topic, and system designers responsible for developing dispatching algorithms used in computer systems, network routers and a variety of other applications.
Jeffrey P. Buzen has been a leader in the field of computer performance analysis since the early 1970's. His career spans an unusually broad range of activities including the creation of fundamental mathematical models and analysis procedures (central server model, convolution algorithm, operational analysis), the development of practical tools based on these theoretical advances (BEST/1, CAPTURE/MVS), and the founding of a commercially successful software company (BGS Systems) that extended, supported and marketed these tools for more than two decades. Throughout his career, he has published extensively, lectured widely and held leadership positions in several professional societies including ACM Sigmetrics, IFIP Working Group 7.3, and CMG.

Jeff Buzen is currently President of the Computer Measurement Group (, a professional society for computer performance practitioners. He also holds a part time appointment as a Consulting Scientist at BMC Software. His Ph.D. in Applied Mathematics is from Harvard University (1971). From 1971 to 1976 he held concurrent appointments as a Lecturer in Computer Science at Harvard and a Systems Engineer at Honeywell. Among his students at Harvard were some of the most influential figures in the computer industry: Robert M. Metcalfe (Ph.D. 1973), inventor of ethernet, John M. McQuillan (Ph.D. 1974), developer of dynamic routing algorithms used in the ARPAnet/Internet, and William H. Gates, co-founder of Microsoft.

In 1975, Jeff Buzen co-founded BGS Systems along with his classmates Robert P. Goldberg and Harold S. Schwenk. He served as Chief Scientist and Senior Vice President at BGS until its merger with BMC Software in 1998.

[Last updated Wed Jan 3 2001]

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