Temporal Prefetcher for Irregular Memory Access Patterns
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Solution Overview
Problem
Existing prefetching techniques are ineffective for workloads with irregular but repeated patterns of memory accesses, such as linked lists, as they rely on observing spatial patterns or constant offsets, leading to poor performance in predicting and prefetching data.
Innovation Solution
A temporal prefetcher that monitors access requests directly from processing circuitry, maintaining correlation information to record observed sequences of memory accesses and prefetching correlated data items based on this information, even during cache hits, to improve data availability and reduce latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing prefetching techniques are used, then spatial patterns and constant offsets can be detected, but irregular but repeated patterns of memory accesses cannot be predicted
Solution Approach 1:
The patent implements a dynamic temporal prefetcher that adapts to different workload patterns by learning from historical access sequences. Unlike static spatial prefetchers, this system dynamically adjusts to irregular but repeated patterns by maintaining correlation information about access sequences, enabling it to handle diverse workloads including linked lists and other non-spatial patterns effectively
Solution Approach 2:
The patent changes the fundamental parameter being monitored from spatial relationships (addresses, offsets) to temporal relationships (access sequences, correlation information). By tracking when data items are accessed rather than where they are located in space, the system can predict irregular but repeated access patterns that spatial methods cannot detect
2Loss of energy
If prefetching is performed only on cache misses, then bandwidth is conserved, but latency is increased for repeated access patterns
Solution Approach 1:
The patent performs preliminary prefetching actions based on temporal correlation information before cache misses occur. By detecting repeated access patterns and predicting future accesses, the system prefetches data in advance during cache hits, eliminating the need to wait for cache misses to trigger prefetching, thus reducing latency without excessive bandwidth consumption
Solution Approach 2:
The patent implements a feedback mechanism where the prefetcher monitors actual access patterns and uses this information to refine its predictions. By continuously learning from observed access sequences and comparing predictions with actual behavior, the system optimizes prefetching decisions to balance bandwidth usage and latency reduction
3Reliability
If correlation information storage is implemented, then temporal patterns can be tracked, but device complexity increases
Solution Approach 1:
The patent segments the prefetching function into distinct components: correlation information storage, pattern detection logic, and prefetch execution. This modular segmentation allows each component to be optimized independently and simplifies the overall design by separating the complex task of temporal pattern recognition into manageable, specialized units
Data Source
AI summary
A technique is provided for prefetching data items. An apparatus has a storage structure with a plurality of entries to store data items. The storage structure is responsive to access requests from processing circuitry to provide access to the data items. The apparatus has prefetch circuitry to prefetch data and correlation information storage to store correlation information for a plurality of data items. The correlation information identifies, for each of the plurality of data items, one or more correlated data items. The prefetch circuitry is configured to monitor the access requests from the processing circuitry. In response to detecting a hit in the correlation information storage for a particular access request that identifies a requested data item for which the correlation information storage stores correlation information, the prefetch circuitry is configured to prefetch the one or more correlated data items identified by the correlation information for the requested data item.