Aperture-Specific Cache Operations for CPU-GPU Coherency Latency
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Solution Overview
Problem
Conventional cache coherency systems in high-performance computing (HPC) systems face inefficiencies and latency issues due to software-managed CPU-GPU coherency, particularly in latency-sensitive systems like ADAS and ADS, and hardware coherency incurs needless overhead for non-coherent memory buffers.
Innovation Solution
Implementing 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 latency and maintaining cache efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware coherency is used for all memory buffers, then cache coherency is maintained, but needless overhead is incurred for non-coherent memory buffers
Solution Approach 1:
The patent applies local quality by differentiating between coherent and non-coherent memory buffers and applying different coherency management strategies to each. Coherent buffers use hardware-managed coherency, while non-coherent buffers use software-managed coherency with explicit flushes and invalidates. This selective approach reduces unnecessary overhead for non-coherent buffers while maintaining coherency where needed.
Solution Approach 2:
The patent segments memory buffers into two distinct categories: coherent buffers and non-coherent buffers. This segmentation allows the system to apply different coherency management mechanisms to each segment, optimizing performance by avoiding hardware coherency overhead for non-coherent buffers while ensuring coherency for coherent buffers.
2Adaptability or versatility
If software-managed CPU-GPU coherency is used, then flexibility is maintained, but latency increases in latency-sensitive systems
Solution Approach 1:
The patent implements dynamic coherency management by switching between hardware-managed and software-managed coherency based on buffer type. For coherent buffers, hardware coherency is used to minimize latency. For non-coherent buffers, software management provides flexibility. This dynamic adaptation allows the system to optimize between performance and flexibility based on actual workload requirements.
3Device complexity
If unified cache coherency operations are applied to all memory, then simplicity is maintained, but destructive interference occurs between coherent and non-coherent cache lines
Solution Approach 1:
The patent applies local quality by treating coherent and non-coherent cache lines differently. By tagging cache lines with coherence status information, the system can selectively apply coherency operations only where needed, preventing destructive interference between coherent and non-coherent cache lines while maintaining operational simplicity through automated classification.
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.