# The ICICS/CS Reading Room

## UBC CS TR-81-16 Summary

- No on-line copy of this technical report is available.

- Optimization Techniques in Computer System Design \& Load Control, September 1981 Prem Swarup Sinha
Analytic modelling has proven to be cost-effective in
the performance evaluation of computer systems. So far,
queueing theory has been employed as the main tool. This
thesis extends the scope of analytic modelling by using
optimization techniques along with queuing theory in
solving the decision-making problems of performance
evaluation. Two different problems have been attempted in
this thesis.
.br
First, a queueing network model is developed to find
the optimal capacities and speeds of the memory levels in a
memory hierarchy system operating in a multiprogrammed
environment. Optimality is defined with respect to mean
system response time under a fixed cost constraint. It is
assumed that the number of levels in the hierarchy as well
as the capacity of the lowest level are known. The effect
of storage management strategy and program behaviour are
characterised by the miss ratio function which, together
with the device technology cost function, is assumed to be
represented by power functions. It is shown that the
solution obtained is globally optimal.
.br
Next, two adaptive schemes, SELF and MULTI-SELF, are
developed to control the flow of jobs in a multiprogrammed
computer system. They periodically determine the number of
jobs from each class that should be activated to minimize
the mean system residence time without saturating the
system. The computation is based on the estimated system
workload in the next interval. An exponential smoothing
technique is used to reduce the error in estimating the
values of the model parameters. The service provided to
each class (specifically, the mean response time) may be
adjusted by changing the weight associated with the job
class. From our simulation results, the schemes appear to
be both stable and robust. Performance improvement over
$S and the Knee
criteria) is significant under some workloads. The
overhead involved in its implementation is acceptable and
the error due to some of the assumptions in the formulation
and solution of the model are discussed.

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