Title :
Adaptive ray packet reordering
Author :
Boulos, Solomon ; Wald, Ingo ; Benthin, Carsten
Author_Institution :
Stanford Univ., Stanford, CA
Abstract :
Modern high-performance ray tracers use large ray packets and SIMD instruction sets to decrease both the computational and bandwidth cost compared to a single ray implementation. Current global illumination renderers, however, are still based around single ray implementations and interfaces. The presumption is that while packets have been shown to work well for highly coherent rays, in the presence of less coherent secondary ray distributions the gains of both packet and SIMD techniques dwindle rapidly. With low enough coherence, performance can be reduced to being as slow as reasonable single ray code - if not worse - so the benefit of packets for a global illumination system is assumed to be next to none. With SIMD width expanding in future architectures, leaving SIMD units underutilized means a massive loss in performance compared to the maximum performance achievable. In this paper, we present a method for recovering packet and SIMD coherence for incoherent secondary ray distributions through demand-driven reordering of rays into more coherent packets. We demonstrate that the reordering overhead is outweighed by the increased coherence within a prototypical implementation in the Manta realtime ray tracer among a wide variety of ray distributions, including diffuse path tracing.
Keywords :
instruction sets; parallel processing; ray tracing; rendering (computer graphics); Manta realtime ray tracer; SIMD instruction set; adaptive ray packet reordering; diffuse path tracing; global illumination rendering; high-performance ray tracing; packet recovery; Bandwidth; Computer aided instruction; Geometry; Layout; Lighting; Performance loss; Ray tracing; Rendering (computer graphics); Sampling methods; Testing;
Conference_Titel :
Interactive Ray Tracing, 2008. RT 2008. IEEE Symposium on
Conference_Location :
Los Angeles, CA
Print_ISBN :
978-1-4244-2741-3
DOI :
10.1109/RT.2008.4634633