GPU Cache Invalidation via Draw Call Tracking
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Solution Overview
Problem
Graphics processing pipelines face inefficiencies due to cache memory management, where dead surfaces occupy space and generate unnecessary memory traffic, as existing systems lack an efficient method to invalidate and reuse cache lines without writing dirty data back to memory.
Innovation Solution
A system comprising a first processor and a second processor, where the application and driver generate a discard surface command to the command processor, which waits for a specific draw call completion before sending an invalidate surface command to the cache, allowing cache lines to be invalidated without writing dirty data back to memory, thereby freeing up space and reducing memory traffic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If cache lines are invalidated without writing dirty data back to memory, then memory traffic is reduced and cache space is freed, but cache consistency and data integrity may be compromised
Solution Approach 1:
The system performs preliminary tracking of surface usage patterns and draw call dependencies before invalidation. The command processor monitors which surfaces are actively being used and determines their validity state in advance, allowing it to safely invalidate only those surfaces that are no longer needed by any subsequent draw calls, thus maintaining cache consistency while enabling aggressive invalidation.
Solution Approach 2:
The system implements a feedback mechanism where the command processor continuously monitors draw call execution and surface usage patterns. Based on this feedback, it dynamically determines which surfaces can be invalidated, ensuring that invalidation decisions are based on actual runtime behavior rather than static assumptions, thereby maintaining reliability while reducing memory traffic.
2Productivity
If cache space is aggressively reused by invalidating surfaces, then cache residency and hit rates improve, but unnecessary data writes may be lost
Solution Approach 1:
The system performs preliminary analysis of draw call dependencies and surface validity states before invalidation. By determining in advance which surfaces will not be needed by future draw calls, the system can safely invalidate their cache lines without losing necessary data, while still aggressively reusing cache space for surfaces that are actively needed, thus improving hit rates without information loss.
3Productivity
If the command processor waits for draw call completion before invalidation, then cache invalidation timing is optimized, but processing latency increases
Solution Approach 1:
The command processor performs preliminary tracking and analysis of draw call execution during normal operation, building up knowledge about surface usage patterns without blocking the rendering pipeline. This preliminary work enables it to make immediate invalidation decisions as soon as surfaces become invalid, optimizing cache timing without introducing significant latency to the overall processing flow.
Data Source
AI summary
Systems, apparatuses, and methods for performing dead surface invalidation are disclosed. An application sends draw call commands to a graphics processing unit (GPU) via a driver, with the draw call commands rendering to surfaces. After it is determined that a given surface will no longer be accessed by subsequent draw calls, the application sends a surface invalidation command for the given surface to a command processor of the GPU. After the command processor receives the surface invalidation command, the command processor waits for a shader engine to send a draw call completion message for a last draw call to access the given surface. Once the command processor receives the draw call completion message, the command processor sends a surface invalidation command to a cache to invalidate cache lines for the given surface to free up space in the cache for other data.