Pre-fetcher Aggressiveness Adaptation for Cache Latency
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Solution Overview
Problem
Conventional pre-fetching algorithms in processor-based systems face difficulties in maintaining cache efficiency due to latency issues and misidentification of sequential memory access patterns, leading to pre-fetchers falling behind in data retrieval and failing to associate non-sequential requests correctly.
Innovation Solution
The method involves modifying the aggressiveness of a pre-fetcher by comparing memory access addresses to a look-ahead window defined by flags, allowing for dynamic adjustment of pre-fetching rates based on cache hits and misses to ensure timely data retrieval and correct stream allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pre-fetcher fetches data aggressively to keep up with memory requests, then data availability improves, but the pre-fetcher may fall behind when cache misses occur due to latency
Solution Approach 1:
The pre-fetcher dynamically adjusts its aggressiveness based on real-time cache hit/miss detection. When a cache miss is detected on a posted pre-fetch address, the pre-fetcher reduces aggressiveness to avoid falling behind. When cache hits occur, it can increase aggressiveness to stay ahead of memory requests. This dynamic adaptation resolves the contradiction between maintaining data availability and managing pre-fetch latency.
Solution Approach 2:
The system implements feedback mechanisms by monitoring cache hit/miss events and using this information to adjust pre-fetch behavior. The detection of cache misses on posted pre-fetch addresses provides feedback that triggers adjustments in pre-fetch aggressiveness, ensuring the pre-fetcher adapts to actual memory access patterns and cache performance, thereby balancing data availability with latency constraints.
2Productivity
If the pre-fetcher uses conventional algorithms to fetch sequential data, then sequential access performance improves, but non-sequential requests with holes or gaps are misidentified and handled incorrectly
Solution Approach 1:
The pre-fetcher applies different handling strategies to different portions of the memory address space. It identifies local patterns of sequential access versus non-sequential access with holes or gaps, and applies appropriate pre-fetch aggressiveness to each. This local quality approach allows the system to maintain high sequential access performance while accurately identifying and correctly handling non-sequential requests, resolving the contradiction between productivity and measurement precision.
Data Source
AI summary
The present invention provides a method and apparatus for adapting aggressiveness of a pre-fetcher in a processor-based system. One embodiment includes modifying a rate for pre-fetching data from a memory into one or more caches by comparing a first address of a memory access request to addresses in an address window that includes one or more previously fetched addresses and one or more addresses to be fetched.