Architectural versus physical solutions for on-chip communication challenges

The growing gap between transistor and global wire speeds in sub-100 nanometer technologies poses numerous challenges to computer architects and circuit designers. This challenge looks to be even more significant in far-future technologies such as molecular-scale wire transmission, whether using carbon nanotubes or quantum dots. While a fixed design scales as its area decreases with feature size reductions, future designs that use a constant area see rapidly increasing global latencies.Two approaches to address these latencies are (1) to use signaling and design techniques to reduce the actual latencies, and (2) to use architectural innovations to reduce the distance that signals must be propagated in the common case. In this talk, after an overview of the communication latency issue, I describe current research that aims to reduce the average distance communicated for processing and memory system signals. For processor designs, I will describe the Static Placement, Dynamic Issue (SPDI) execution model, which allows the compiler to place dependent instructions near one another, and which is being implemented in the TRIPS processor. I will also describe Non-Uniform Caches Access (NUCA) designs, which attempt to reduce average signal distance for cache accesses.