Region-Aware Delta Prefetching for Irregular Cache Access
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing memory prefetching techniques face challenges in achieving accurate and cost-effective prefetching into the innermost cache due to prohibitive storage requirements and inadequate prediction of irregular access patterns, leading to reduced coverage and increased latency in high-performance cores.
Innovation Solution
A region aware delta prefetcher that combines spatial and temporal components to learn multiple frequently occurring deltas per large address region, using a subregion buffer and pattern table to track and apply these deltas efficiently, thereby enhancing prefetch accuracy and coverage while maintaining low hardware costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional memory prefetching techniques are used to predict and fetch data before access, then fetch operation speed is improved, but storage requirements become prohibitive and coverage is reduced for irregular access patterns
Solution Approach 1:
The patent segments the address space into multiple regions and uses separate buffer structures (spatial buffer, temporal buffer, region buffer) for each segment. This allows the system to track access patterns in a distributed manner rather than requiring a single large storage structure, thereby reducing overall storage requirements while maintaining prefetching capability across the entire address space.
Solution Approach 2:
The patent applies different prefetching strategies to different regions of the address space based on their access patterns. By analyzing access patterns locally in each region and applying appropriate prefetching only where needed, the system improves fetch speed for irregular access patterns without uniformly increasing storage requirements across all memory regions.
2Loss of time
If prefetching is implemented to reduce latency, then performance is enhanced, but hardware cost increases due to additional buffer structures and complexity
Solution Approach 1:
The patent merges spatial prefetching and temporal prefetching into a unified region-aware delta prefetcher architecture. By combining these two approaches and sharing buffer structures across regions, the system reduces redundant hardware components while maintaining the latency-reduction benefits of both spatial and temporal prefetching strategies.
Solution Approach 2:
The region buffer structure serves multiple functions: it tracks accessed regions, stores region identifiers, and coordinates between spatial and temporal prefetching mechanisms. This multi-functionality reduces the need for separate dedicated structures for each function, thereby lowering overall hardware cost while maintaining effective prefetching.
3Measurement precision
If multiple prefetching strategies are combined to improve coverage, then prefetching accuracy is improved, but device complexity increases
Solution Approach 1:
The patent implements a nested buffer architecture where spatial buffers and temporal buffers are contained within region buffers. This hierarchical nesting allows the system to maintain multiple prefetching strategies simultaneously while organizing them in a structured manner that reduces overall complexity compared to having separate independent structures for each strategy.
Data Source
AI summary
An apparatus includes memory circuitry including a first data structure and prefetch circuitry that is coupled to the memory circuitry. The prefetch circuitry is to store, in the first data structure, a first subregion entry corresponding to a first subregion of a memory region allocated to a program. The first subregion entry is to include a plurality of delta values. A first delta value of the plurality of delta values represents a first distance between two cache lines associated with consecutive memory accesses within a second subregion of the memory region. The prefetch circuitry is further to detect a first memory access of a first cache line in the first subregion, identify prefetch candidates based on the first cache line and the plurality of delta values, and issue at least one prefetch request based on at least two of the prefetch candidates to be prefetched into a cache.