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The Data Diffusion Machine with a Scalable Point-to-Point Network

Henk L. Muller, Paul W. A. Stallard, David H. D. Warren, The Data Diffusion Machine with a Scalable Point-to-Point Network. CSTR-93-17, Department of Computer Science, University of Bristol. October 1993. PDF, 131 Kbytes.


The Data Diffusion Machine (DDM) is a virtual shared memory machine. Data items in the machine have no fixed home location but instead migrate to the processors that are actually using the data. Coherency is maintained with a hierarchical directory scheme. In an uncongested machine, all memory operations complete in a time bounded by the logarithm of the number of processors. As the machine load increases, the natural combining of the DDM hierarchy allows better network utilisation and helps improve performance. This paper proposes an implementation of the DDM with split directories interconnected with a point-to-point network. This is easier to construct and scales better than previous designs. The protocol has been redesigned for this intercoonect. The network provides a number of paths between pairs of processors and the protocol maintains sequential consistency under these conditions. Conflicting requests (writes on different processors to the same data item) are resolved in a time bounded by the number of processors, without chance of starvation. Performance measurements for systems of up to 81 processors show promising results.

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