| Summary: | Load balancing has been a topic of interest in both academia and industry, mainly
because of the scope for performance enhancement that is available to be exploited in
many parallel and distributed processing environments. Among the many approaches
that have been used to solve the load balancing problem, we find that only very few
use prediction of code execution times. Our reasoning for this is that the field of code prediction
is in its infancy. As of this writing, we are not aware of any prediction-based
load balancing approach that uses prediction8 of code-execution times, and uses neither
the information provided by the user, nor an off-line step that does the prediction, the
results of which are then used at run-time. In this context, it is important to note that
prior studies have indicated the feasibility of predicting the CPU requirements of general
application programs.
Our motivation in using prediction-based load balancing is to determine the feasibility
of the approach. The reasoning behind that is the following: if prediction-based load
balancing does yield good performance, then it may be worthwhile to develop a predictor
that can give a rough estimate of the length of the next CPU burst of each process. While
high accuracy of the predictor is not essential, the computation overhead of the predictor
must be sufficiently' small, so as not to offset the gain of load balancing.
As for the system, we assume a set of autonomous computers, that are connected by
a fast, shared medium. The individual nodes can vary in the additional hardware and
software that may be available in them. Further, we assume that the processes in the
workload are sequential.
The first step is to fix the parameters for our assumed predictor. Then, an algorithm
that takes into account the characteristics of the predictor is proposed. There are many
trade-off decisions in the design of the algorithm, including certain steps in which we
have relied on trial and error method to find suitable values. The next logical step is
to verify the efficiency of the algorithm. To assess its performance, we carry out event
driven simulation. We also evaluate the robustness of the algorithm with respect to the
characteristics of the predictor.
The contribution of the thesis is as follows: It proposes a load-balancing algorithm
for a heterogeneous cluster of workstations connected by a fast network. The simulation
assumes that the heterogeneity is limited to variability in processor clock rates; but
the algorithm can be applied when the nodes have other types of heterogeneity as well.
The algorithm uses prediction of CPU burst lengths as its basic input unit. The performance
of the algorithm is evaluated through event driven simulation using assumed
workload distributions. The results of the simulation show that the algorithm yields a
good improvement in response times over the scenario in which no load redistribution is
done.
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