Ray-by-Ray improves GPU ray tracing performance with fine-grained control
Ray-by-Ray: Fine-Grained Resource Management for GPU Ray Tracing Units
Hardware Architecture
Summary
Rendering realistic images with ray tracing on GPUs can be slow because each light ray behaves differently, making it hard for hardware to handle many rays efficiently at once. The researchers found that current GPU designs waste resources due to this mismatch between how rays are processed and how hardware threads work together. They created Ray-by-Ray, a way to manage each ray individually to better share the hardware, improving speed without needing bigger memory buffers. Their tests showed this approach nearly doubles performance with very little extra hardware cost.
What this means in practice
- •For graphics engine developers: Increase real-time ray tracing performance in game and film rendering engines by using Ray-by-Ray’s fine-grained buffer management techniques.
- •For gpu hardware designers: Incorporate Ray-by-Ray concepts into future GPU ray tracing unit designs to improve utilization and throughput without significantly increasing area.
Authors
Junrui Pan, Cesar Avalos Baddouh, Kai Ze Ee, Timothy G. Rogers
Abstract
Ray tracing (RT) generates photorealistic images by simulating the physical behavior of light as it interacts with surfaces in a virtual scene. In film production and high-end rendering pipelines, this technique computes global illumination, reflections, refractions, and soft shadows by tracing millions of light rays per frame and accurately modeling their bounces and attenuation. Contemporary GPUs incorporate specialized ray tracing hardware to accelerate key operations in the traversal pipeline. By accelerating these stages in hardware, the unit enables real-time ray tracing for complex scenes that previously required offline computation. However, ray tracing introduces substantial control and data divergence. Each ray may traverse a different set of nodes in the acceleration structure, encounter distinct materials, or terminate at varying depths. This irregularity reduces thread coherence and exposes a fundamental disparity between the GPU SIMT and per-thread execution model of dedicated RT units, where each ray progresses independently. In this work, we seek to validate assumptions made in open-source infrastructure and identify potential inefficiencies in resource management within the ray tracing pipeline. To address inefficiency caused by mismatches between SIMT and RT granularities, we propose Ray-by-Ray, which decomposes on-chip buffers into the granularity of individual rays and introduces lightweight management structures that enable more warps to run in parallel without increasing buffer capacity. This approach improves ray tracing unit utilization and increases memory-level parallelism. Experimental results show that Ray-by-Ray achieves an average performance improvement of 1.91x over the baseline, with an area overhead of 0.19\%.