Efficient MIMD architectures for high-performance ray tracing

Ray tracing efficiently models complex illumination effects to improve visual realism in computer graphics. Typical modern GPUs use wide SIMD processing, and have achieved impressive performance for a variety of graphics processing including ray tracing. However, SIMD efficiency can be reduced due to the divergent branching and memory access patterns that are common in ray tracing codes. This paper explores an alternative approach using MIMD processing cores custom-designed for ray tracing. By relaxing the requirement that instruction paths be synchronized as in SIMD, caches and less frequently used area expensive functional units may be more effectively shared. Heavy resource sharing provides significant area savings while still maintaining a high MIMD issue rate from our numerous light-weight cores. This paper explores the design space of this architecture and compares performance to the best reported results for a GPU ray tracer and a parallel ray tracer using general purpose cores. We show an overall performance that is six to ten times higher in a similar die area.