Paper Details

The Investigation of Communications Patterns in Occam Programs

Authors: Candlin, Rosemary, Luo, Qiangyi, Skilling, Neil

Abstract:

The performance of a concurrent computation running on a multiprocessor system may depend critically on the way in which the program is decomposed and placed on the machine. In order to exploit the potential of parallel processors, it is necessary to balance the advantage of spreading the computational load as thinly as possible over the processors, with the disadvantage that increased communication delays may slow down the computation. In general, there is no satisfactory theoretical model of the complex interaction between the amount of computation carried out by the individual processes, their frequency of communication and the topology of the underlying machine. For many programs, it is not easy to see in advance how computation will interact with communication, and placement strategies which depend only on a static analysis of the program structure may not be sufficient. The work described here is an attempt to provide useful tools for the occam programmer which can be used to investigate communications patterns, and to explore different configurations rapidly.We think that this approach will be particularly valuable for programs which can be decomposed in a natural way into a fairly large number of top-level occam processes, so that the preliminary parallelization arises out of the nature of the application, and the main problem is to place these processes on a smaller number of physical processors. This is often the case for programs which model real-time systems, and we have taken as an example an application from chemical engineering. In programs like this, there is natural concurrency in the real world which can be easily represented in terms of occam processes. At the moment, we do not attempt to extract parallelism automatically, or handle shared data, though there are a number of systems that have tackled these problems (see, for example [1] and [2]). Our main aim at this stage is to provide a programmer with profiling tools, and see to what extent they can help to produce an efficient implementation of the program.

Proceedings:

OUG-11: Developing Transputer Applications, J. Wexler, 1989, pp 99 - 108 published by IOS Press, Amsterdam

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