BVH Parallel Traversal With Synchronized Thread Order
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Solution Overview
Problem
Current ray tracing methods in 3D computer graphics suffer from inefficiencies due to code divergence and data divergence in GPU-based bounding volume hierarchy (BVH) traversal, leading to reduced performance and increased computational intensity.
Innovation Solution
Implement non-divergent parallel traversal operations for BVH using cross-group operations to synchronize thread traversal, allowing threads to follow a uniform order and share data, thereby reducing code and data divergence and improving traversal speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If divergent parallel traversal is used for BVH, then each thread can independently follow its own traversal path, but code divergence and data divergence occur leading to reduced performance and increased computational intensity
Solution Approach 1:
Instead of allowing each thread to independently choose its traversal path (divergent approach), the patent inverts the approach by forcing all threads to follow the same traversal path (uniform approach). This is achieved by having threads synchronize on a common traversal stack and process nodes in a predetermined order, eliminating code and data divergence while maintaining traversal completeness.
Solution Approach 2:
The patent applies homogeneity by making all threads execute identical instructions in the same order during BVH traversal. Threads are forced to follow a uniform traversal path through the BVH, processing nodes in the same sequence. This homogeneous execution eliminates the code divergence and data divergence that plague divergent parallel approaches, significantly improving GPU utilization and traversal speed.
2Ease of operation
If threads follow different traversal paths in parallel, then individual ray processing is optimized, but data divergence causes wasted processor cycles
Solution Approach 1:
The patent inverts the conventional approach by not allowing threads to independently optimize their own traversal paths. Instead, all threads are constrained to follow the same predetermined traversal path through the BVH. This uniform approach eliminates data divergence, ensuring that all threads access the same data at the same time, thereby eliminating wasted processor cycles from divergent memory access patterns.
3Productivity
If uniform traversal order is enforced across all threads, then code divergence is eliminated, but threads may wait for each other reducing parallel efficiency
Solution Approach 1:
The patent segments the traversal work into discrete node processing tasks that can be efficiently distributed across threads. By organizing the BVH traversal as a series of node visits with associated ray-testing tasks, the uniform traversal path does not force threads to wait idle. Instead, threads can efficiently process assigned nodes and associated rays without synchronization barriers, eliminating both code divergence and thread waiting time.
Data Source
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AI summary
Various approaches to performing non-divergent parallel traversal operations for a bounding volume hierarchy ("BVH") during ray tracing are presented. For example, a computer system has a processing unit with threads that, collectively, perform ray tracing for a group of rays in parallel in a computer-represented environment, which includes geometric objects (such as triangles) enclosed in the BVH. Each of the threads receives parameters for a given ray and traverses the BVH to determine an intersection, if any, between the given ray and one of the geometric objects. The order of traversal of the BVH is synchronized between threads for the rays of the group, for example, using a cross-group operation such as a ballot operation. In this way, the overall speed of the BVH traversal can be improved in many cases, while avoiding code divergence and data divergence in extra-wide single-instruction, multiple data ("SIMD") graphics processing unit ("GPU") architectures.