from the city of Vienna: Notes on SPMD architecture VIII

Conclusion.

Crew is life, everything else is just details

Anonymous

This post reviews and rewrites the initial requirements for the Architecture model stated in the post "Requirements" in the light of the description and characterization of the model carried out throughout the series.

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As was stated as an initial requirement in the aforementioned post, three different types of transfers among nodes have to be supported, these are the Data distribution, Data collection and Data redistribution transferences. The first two are necessary in the case of working on Local memory and the three of them, where performing a 2-D processing on Distributed memory.

Additionally, the initial no-data-loss requirement stated in the aforementioned post, has lead to a lower lever requirement concerning every Data transference that consists on supporting flow control at data block level.

On the other hand, as has been shown throughout this series, a minimum number of memory buffers for the data transferences is necessary in order to allow the nodes to work at the maximum Throughput as well as in order to avoid data-loss.

With respect to achieving maximum Throughput, this number may vary depending on the processing (1-D or 2-D) and the working load of the nodes over time (steady or non-steady).

Certainly, as was shown in the post "Local and Distributed memory processing in steady workload" of this series, a different number of buffers is necessary for the nodes to achieve maximum Throughput when performing 1-D or 2-D processing.

Otherwise, in what concerns to no-data-loss, as was shown in the previous post "Operation in non-steady workload", memory buffers allow the node to temporarily not to lose input data when the processor can not process input data units at the rate required by the input device; similarly, they allow the node to temporarily not lose output data when the output device can not send output data units at the rate required by the processor.

In order to adequate the number of processing nodes to the necessities –in terms of memory and/or Throughput– of the processing, the Architecture model has to be scalable.

According to all the above, the requirements for the Architecture model can, finally, be stated as follows:

For the Architecture model, it must be possible to define the number of processing nodes.

For each node, it must be possible to define the necessary transfers. The different types of transfers are the Data distribution transfer, the Data collection and the Data redistribution transfer. All of them have to support flow control at data block level.

For each transfer, it must be possible to define the necessary number of buffers for both input and output.

In the writing of this article, Heroes del Silencio (Mar adentro, April 1992 Munich (Germany)) have collaborated in an involuntary but decisive way.