GPU Ray Tracing Scheduling Hints to Prevent Cache Thrashing
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Solution Overview
Problem
Existing graphics processing units (GPUs) face inefficiencies in cache management due to the allocation of a larger number of rays than the ray intersect accelerator can handle, leading to cache thrashing and reduced performance in ray tracing tasks.
Innovation Solution
Incorporating a hint-based scheduling mechanism in shader programs, where the 'intersect_ray_soon' hint adjusts thread priority and resource allocation based on the availability of the ray intersect accelerator, preventing cache pollution and optimizing memory usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a larger number of rays are allocated in cache to increase parallel processing capacity, then the GPU can handle more ray tracing operations, but cache thrashing occurs and performance decreases
Solution Approach 1:
The patent implements dynamic resource allocation where the ray tracing system adjusts the number of rays allocated to the ray intersect accelerator based on real-time resource availability and workload conditions. The hint-based scheduling mechanism allows the system to dynamically modify thread priority and resource allocation, preventing cache thrashing by ensuring that ray data allocation matches the actual processing capacity of the accelerator at any given moment.
Solution Approach 2:
The system employs feedback through hint-based scheduling where the ray tracing shader provides hints about upcoming ray intersect operations. This feedback mechanism allows the scheduler to anticipate resource needs and adjust allocation accordingly, preventing both cache pollution from over-allocation and under-utilization of available processing capacity.
2Speed
If ray data is allocated in cache before ray intersect accelerator invocation, then memory access is prepared in advance, but cache pollution occurs when accelerator capacity is exceeded
Solution Approach 1:
The patent applies preliminary action through hint-based scheduling where the system prepares ray data allocation in advance based on hints from the shader about upcoming ray intersect operations. By processing these hints before actual ray tracing execution, the scheduler can pre-allocate appropriate cache resources without exceeding accelerator capacity, thus maintaining fast memory access while preventing cache pollution.
3Productivity
If thread priority is adjusted based on ray intersect accelerator availability, then resource utilization is optimized, but scheduling complexity increases
Solution Approach 1:
The patent introduces an intermediary hint-based scheduling mechanism that sits between the ray tracing shader and the ray intersect accelerator. This intermediary layer processes hints from the shader and translates them into priority adjustments and resource allocation decisions, simplifying the overall scheduling complexity while maintaining optimized resource utilization. The hint system acts as a mediator that coordinates between different components without requiring complex direct communication.
Data Source
AI summary
Techniques are disclosed relating to graphics processor that support ray tracing. In particular, shader circuitry may be configured to adjust a scheduling priority of a single-instruction multiple-data (SIMD) group of a shader program based on a hint that the SIMD group has an upcoming ray intersect command for ray intersect accelerator circuitry and based on a resource usage indication from the ray intersect accelerator circuitry. This may advantageously reduce cache thrashing, e.g., when shaders may allocate memory for ray intersect commands and fill a shared cache faster than the ray intersect accelerator circuitry can process the rays.