Fine-Grained Cache Prefetching with Side-Buffer Sub-Cache Lines
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Solution Overview
Problem
Conventional prefetch mechanisms in modern processors operate at cache line granularity, failing to exploit the benefits of fine-grained memory architectures that support sub-cache line data chunks, leading to inefficiencies in energy consumption and bandwidth utilization, particularly for irregular workloads.
Innovation Solution
A fine-grained memory aware prefetcher that fetches atom-sized data chunks, stored in a side buffer, to support sub-cache line granularity, enabling efficient prefetching for irregular workloads without requiring changes to the existing cache hierarchy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional prefetch mechanisms operate at cache line granularity, then the existing cache hierarchy is maintained, but energy efficiency and bandwidth utilization deteriorate for fine-grained memory architectures
Solution Approach 1:
The patent segments the cache line into multiple sub-cache lines (e.g., 4-byte, 8-byte, or 16-byte atoms). Instead of treating the entire 64-byte cache line as a single unit, the prefetcher divides it into finer granularities that match the underlying fine-grained memory architecture. This segmentation enables selective prefetching of only the necessary sub-cache lines, reducing energy consumption and improving bandwidth utilization while maintaining compatibility with the existing cache hierarchy.
Solution Approach 2:
The patent applies local quality by making different parts of the cache line have different prefetching characteristics. Each sub-cache line can be independently identified and prefetched based on its specific access patterns and requirements. This allows the system to optimize prefetching for specific regions (e.g., frequently accessed atoms) while avoiding unnecessary prefetching of other regions, thereby improving energy efficiency without requiring a complete overhaul of the prefetch mechanism.
2Speed
If prefetching is performed at cache line granularity, then device simplicity is maintained, but memory access latency increases for irregular workloads
Solution Approach 1:
The patent segments the cache line into multiple sub-cache lines (e.g., 4-byte, 8-byte, or 16-byte atoms). Instead of treating the entire 64-byte cache line as a single unit, the prefetcher divides it into finer granularities that match the underlying fine-grained memory architecture. This segmentation enables selective prefetching of only the necessary sub-cache lines, reducing energy consumption and improving bandwidth utilization while maintaining compatibility with the existing cache hierarchy.
Solution Approach 2:
The patent introduces dynamic atom size selection, where the prefetcher can adaptively choose the appropriate atom size (4 bytes, 8 bytes, or 16 bytes) based on the access patterns detected during training. This dynamic adjustment allows the system to optimize for different workload types (e.g., graph applications, array of pointers) without requiring a fixed complex structure, thereby improving memory access speed while keeping the prefetcher design manageable.
3Productivity
If sub-cache line granularity is supported, then energy efficiency and bandwidth utilization improve, but the existing cache hierarchy requires modification
Solution Approach 1:
The patent introduces a side buffer as an intermediary component between the prefetcher and the existing cache hierarchy. The side buffer stores the prefetched sub-cache line data (atoms) before they are transferred to the main cache. This intermediary structure allows the system to support fine-grained prefetching without requiring fundamental modifications to the existing cache hierarchy, as the side buffer acts as a buffer zone that bridges the granularity mismatch between sub-cache lines and full cache lines.
Solution Approach 2:
The patent segments the cache line into multiple sub-cache lines (e.g., 4-byte, 8-byte, or 16-byte atoms). Instead of treating the entire 64-byte cache line as a single unit, the prefetcher divides it into finer granularities that match the underlying fine-grained memory architecture. This segmentation enables selective prefetching of only the necessary sub-cache lines, reducing energy consumption and improving bandwidth utilization while maintaining compatibility with the existing cache hierarchy.
Data Source
AI summary
A fine-grained memory aware cache prefetch is described. In one or more implementations, a processor includes a cache. The cache includes one or more cache lines that each include one or more sub-cache lines. The processor also includes a side buffer configured to store prefetched sub-cache line data for storage in the one or more sub-cache lines. The processor also includes a fine-grained memory aware prefetcher associated with the cache. The fine-grained memory aware prefetcher includes fine-grained prefetch logic that, when executed, causes the fine-grained memory aware prefetcher to generate a fine-grained prefetch request directed to a fine-grained memory. The fine-grained prefetch request identifying data to be prefetched from the fine-grained memory. Responsive to the fine-grained prefetch request, the fine-grained memory aware prefetcher receives the data from the fine-grained memory and stores the data in the side buffer as the prefetched sub-cache line data for retrieval by the cache.