Aperture-Specific Cache Operations for CPU-GPU Coherency
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Solution Overview
Problem
Conventional cache coherency systems in high-performance computing (HPC) systems incur latency and performance issues due to ambiguous memory addressing and unnecessary overhead in CPU-GPU communication, particularly in latency-sensitive applications like ADAS and ADS, as they manage cache coherency through software mechanisms that are inefficient and time-consuming.
Innovation Solution
Implement aperture-specific cache management operations to differentiate between coherent and non-coherent system memory buffers, using hardware-managed coherency for coherent buffers and explicit flushes/invalidates for non-coherent buffers, thereby reducing unnecessary cache line targeting and maintaining critical cache lines for performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If software mechanisms are used to manage cache coherency in CPU-GPU communication, then cache coherency can be maintained, but latency and performance deteriorate due to unnecessary overhead and time-consuming operations
Solution Approach 1:
The patent segments the memory addressing space into aperture-specific regions, allowing different cache management strategies for different memory apertures. This enables selective coherency management rather than uniform treatment of all memory, reducing unnecessary coherency operations and associated latency overhead.
Solution Approach 2:
The patent applies different cache management qualities to different memory apertures - some apertures use hardware-managed coherency while others use explicit flush/invalidate operations. This local differentiation optimizes performance by applying the appropriate coherency strategy to each memory region based on its access patterns and requirements.
2Reliability
If conventional cache coherency systems perform explicit flushes and invalidates for all cache lines, then cache coherency is maintained, but performance deteriorates due to unnecessary operations on critical cache lines
Solution Approach 1:
Instead of performing complete cache flushes and invalidates for all cache lines, the patent applies partial actions by targeting only specific apertures or subsets of cache lines that require coherency management. This selective approach maintains necessary coherency while avoiding excessive operations on critical or frequently accessed cache lines.
Solution Approach 2:
The patent extracts and separates coherent and non-coherent memory apertures into distinct management categories. By taking out the coherency management function from uniform treatment and applying it only where necessary, the system eliminates unnecessary operations and improves overall performance.
3Device complexity
If unified cache management is applied to all memory buffers, then implementation is simplified, but destructive interference occurs between coherent and non-coherent cache lines
Solution Approach 1:
The patent segments the cache management system into aperture-specific handlers that distinguish between coherent and non-coherent memory buffers. This segmentation prevents destructive interference by applying appropriate management strategies to each buffer type independently, while maintaining manageable complexity through systematic organization.
Solution Approach 2:
The patent introduces aperture identifiers and classification mechanisms as intermediaries between memory access operations and cache management. These intermediaries mediate the interaction by routing coherent and non-coherent cache lines to appropriate management paths, preventing harmful interference while organizing complexity systematically.
Data Source
AI summary
A processing device including a first cache is coupled to a system memory and a parallel processing unit (PPU) including a second cache. An operation to modify cache lines of the second cache associated with a first aperture of the system memory is received. A first subset of cache lines of the second cache is identified. The first subset of cache lines is associated with the first aperture of the system memory and is different from a second subset of cache lines of a second aperture of the system memory. The first subset of cache lines is modified as specified by the cache operation.