Report Number: CS-TR-74-435
Institution: Stanford University, Department of Computer Science
Title: Balanced computer systems.
Author: Price, Thomas G.
Date: April 1974
Abstract: We use the central server model to extend Buzen's results on
balance and bottlenecks. We develop two measures which appear
to be useful for evaluating and improving computer system
performance. The first measure, called the balance index, is
useful for balancing requests to the peripheral processors.
The second quantity, called the sensitivity index, indicates
which processing rates have the most effect on overall system
We define the capacity of a central server model as the
maximum throughput as we vary the peripheral processor
probabilities. We show that the reciprocal of the CPU
utilization is a convex function of the peripheral processor
probabilities and that a necessary and sufficient condition
for the peripheral processor probabilities to achieve
capacity is that the balance indexes are equal for all
peripheral processors. We give a method to calculate capacity
using classical optimization techniques.
Finally, we consider the problem of balancing the processing
rates of the processors. Two conditions for "balance" are
derived. The first condition maximizes our uncertainty about
the next state of the system. This condition has several
desirable properties concerning throughput, utilizations,
overlap, and resistance to changes in job mix. The second
condition is based on obtaining the most throughput for a