Collet J H, Litaize D, Van Campenhout J, Jesshope C, Desmulliez M, Thienpont H, Goodman J, Louri A
Laboratoire d'Analyse et d'Architecture des Systèmes du Centre National de la Recherche Scientifique, 7 avenue du colonel Roche, F-31077 Toulouse, France.
Appl Opt. 2000 Feb 10;39(5):671-82. doi: 10.1364/ao.39.000671.
The relevance of introducing optical interconnects (OI's) in monoprocessors and multiprocessors is studied from an architectural point of view. We show that perhaps the major explanation for why optical technologies have nearly been unable to penetrate into computers is that OI's generally do not shorten the memory-access time, which is the most critical issue for today's stored-program machines. In monoprocessors the memory-access time is dominated by the electronic latency of the memory itself. Thus implementing OI's inside the memory hierarchy without changing the memory architecture cannot dramatically improve the global performance. In strongly coupled multiprocessors the node-bypass latency dominates. Therefore the higher the connectivity (possibly with optics), the shorter the path to another node, but the more expensive the network and the more complex the structure of electronic nodes. This relation leaves the choice of the best network open in terms of simplicity and latency reduction. The bottlenecks resulting from and the benefits of implementing OI's are discussed with respect to symmetric multiprocessors, rings, and distributed shared-memory supercomputers.
从架构角度研究了在单处理器和多处理器中引入光互连（OI）的相关性。我们表明，光学技术几乎无法渗透到计算机中的主要原因可能是，OI通常无法缩短内存访问时间，而内存访问时间是当今存储程序机器最关键的问题。在单处理器中，内存访问时间主要由内存本身的电子延迟决定。因此，在不改变内存架构的情况下在内存层次结构内部实现OI并不能显著提高整体性能。在强耦合多处理器中，节点旁路延迟占主导。因此，连接性越高（可能采用光学方式），到另一个节点的路径就越短，但网络成本越高，电子节点的结构也越复杂。这种关系使得在简单性和延迟降低方面选择最佳网络的问题悬而未决。针对对称多处理器、环形结构和分布式共享内存超级计算机，讨论了实施OI所导致的瓶颈和带来的好处。
