RT Journal Article
JF IEEE Transactions on Visualization & Computer Graphics
YR 2012
VO 18
IS
SP 1438
TI Combining Single and Packet-Ray Tracing for Arbitrary Ray Distributions on the Intel MIC Architecture
A1 M. Ernst,
A1 S. Woop,
A1 I. Wald,
A1 C. Benthin,
A1 W. R. Mark,
K1 ray tracing
K1 multiprocessing systems
K1 parallel architectures
K1 Intel many integrated core architecture
K1 packet-ray tracing
K1 arbitrary ray distributions
K1 Intel MIC architecture
K1 traversal stack
K1 SIMD lane
K1 SIMD utilization
K1 multiple incoherent streams
K1 memory accesses
K1 single-ray tracing scheme
K1 16-wide SIMD hardware
K1 bounding-volume hierarchy
K1 branching factor
K1 primitive intersection test
K1 hybrid tracing scheme
K1 Kernel
K1 Vectors
K1 Ray tracing
K1 Registers
K1 Memory management
K1 Hardware
K1 SIMD processors.
K1 Ray tracing
AB Wide-SIMD hardware is power and area efficient, but it is challenging to efficiently map ray tracing algorithms to such hardware especially when the rays are incoherent. The two most commonly used schemes are either packet tracing, or relying on a separate traversal stack for each SIMD lane. Both work great for coherent rays, but suffer when rays are incoherent: The former experiences a dramatic loss of SIMD utilization once rays diverge; the latter requires a large local storage, and generates multiple incoherent streams of memory accesses that present challenges for the memory system. In this paper, we introduce a single-ray tracing scheme for incoherent rays that uses just one traversal stack on 16-wide SIMD hardware. It uses a bounding-volume hierarchy with a branching factor of four as the acceleration structure, exploits four-wide SIMD in each box and primitive intersection test, and uses 16-wide SIMD by always performing four such node or primitive tests in parallel. We then extend this scheme to a hybrid tracing scheme that automatically adapts to varying ray coherence by starting out with a 16-wide packet scheme and switching to the new single-ray scheme as soon as rays diverge. We show that on the Intel Many Integrated Core architecture this hybrid scheme consistently, and over a wide range of scenes and ray distributions, outperforms both packet and single-ray tracing.
PB IEEE Computer Society, [URL:http://www.computer.org]
SN 1077-2626
LA English
DO 10.1109/TVCG.2011.277
LK http://doi.ieeecomputersociety.org/10.1109/TVCG.2011.277