Issei Kino

Approximation methods for two-layer queueing models

We discuss methods to calculate performance measures of queueing models with simultaneous resource possession in which customers who possess different types of passive resources compete with other customers for the same active resources. In this paper, we propose a two-layer queueing model which can adequately model such systems and two extended flow-equivalent methods for approximating the performance measures of two-layer models. We give an example of the model, and we describe the results of a study of the accuracy of the approximation methods.

Probabilistic Analysis of Barrier Eliminating Method Applied to Load-Imbalanced Parallel Application

In order to reduce the overhead of barrier synchronization, we have proposed an algorithm which eliminates barrier synchronizations and evaluated its validity experimentally in our previous study. As a result, we have found that the algorithm is more effective to the load-imbalanced program than load-balanced program. However, the degree of the load balance has not been discussed quantitatively. In this paper, we model the behavior of parallel programs. In our model, the execution time of a phase contained in a parallel program is represented as a random variable. To investigate how the degree of the load balance influences the performance of our algorithm, we varied the coefficient of variation of probability distribution which the random variable follows. Using the model, we evaluated the execution time of parallel programs and found that theoretical results are consistent with experimental ones.