Hardware Stream Prefetcher Dynamic Look-Ahead Distance Adjustment
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Solution Overview
Problem
Existing prefetch buffer systems face challenges in determining an optimal look-ahead distance that adequately supports software processes with varying data usage rates, leading to potential delays or premature data eviction.
Innovation Solution
A system comprising a memory, counters, and a control circuit that adjusts the prefetch look-ahead distance based on cache miss and hit counters, incrementing the offset value when cache misses occur and resetting counters when thresholds are met, allowing for dynamic adaptation to different data usage patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the prefetch look-ahead distance is increased to support rapid data consumption processes, then data availability for fast processes improves, but data staleness and premature eviction occur for slow processes
Solution Approach 1:
The patent implements dynamic adjustment of the prefetch look-ahead distance by monitoring cache hit/miss ratios and adapting the prefetch distance accordingly. The system transitions from a static fixed look-ahead distance to a dynamic variable distance that automatically adjusts based on actual memory access patterns, resolving the contradiction between supporting fast and slow data consumption processes
Solution Approach 2:
The patent changes the parameter of prefetch look-ahead distance from a fixed value to a variable value that can be adjusted based on cache performance metrics. By monitoring cache hit/miss ratios and modifying the prefetch distance parameter dynamically, the system optimizes data prefetching for different process data consumption rates without causing data staleness
2Reliability
If the prefetch look-ahead distance is decreased to prevent data staleness, then data freshness improves, but processor execution pauses occur due to insufficient data availability
Solution Approach 1:
The system dynamically adjusts the prefetch look-ahead distance based on monitored cache performance, allowing the distance to expand when cache hits are frequent (indicating slow data consumption) and contract when cache misses increase (indicating fast data consumption). This dynamic behavior prevents both data staleness and processor execution pauses
Solution Approach 2:
The patent implements a feedback mechanism that monitors cache hit/miss ratios and uses this information to adjust the prefetch look-ahead distance. The feedback loop continuously adapts the prefetching behavior to match actual memory access patterns, ensuring data freshness while maintaining sufficient data availability to prevent processor pauses
3Device complexity
If a fixed prefetch limit is used to simplify buffer management, then system complexity is reduced, but adaptability to varying data usage rates is lost
Solution Approach 1:
The patent implements a self-service mechanism where the prefetch buffer automatically monitors its own performance through cache hit/miss ratio monitoring and autonomously adjusts the prefetch look-ahead distance without external intervention. This self-adjusting capability provides adaptability to varying data usage rates while maintaining relatively simple buffer management structure
Solution Approach 2:
The system changes the prefetch limit parameter from a fixed value to a dynamically adjustable value based on cache performance metrics. This parameter change enables the buffer to adapt to different data usage rates while the adjustment mechanism remains integrated within the existing buffer management framework, minimizing additional complexity
Data Source
AI summary
An apparatus for prefetching data for a processor is presented. The apparatus may include a memory, a first counter, a second counter, and a control circuit. The memory may include a table with at least one entry in which the at least one entry may include an expected address of a next memory access and a next address from which to fetch data, wherein the next address is an offset value different from the expected address. The at least one entry may also include a maximum limit for the offset value. The first counter may increment responsive to an address of a memory access matching the expected address. The second counter may increment responsive to the address of the memory access resulting in a cache miss. The control circuitry may be configured to increment the maximum value of the offset value dependent upon a value of the second counter.