L1 Cache Hazard Handling for Inflight Prefetch Demand Requests
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Solution Overview
Problem
Existing prefetch techniques in digital data processors face inefficiencies due to cache hazards where a demand fetch occurs while a prefetch is pending, leading to redundant operations and increased electrical power consumption in detecting cache misses.
Innovation Solution
A cache system that detects cache hazards by determining the allocated cache way upon a miss and comparing it to demand request addresses only when necessary, reducing unnecessary power consumption by minimizing address comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a demand fetch occurs while a prefetch is pending, then the cache system services the demand request, but redundant operations occur and electrical power consumption increases
Solution Approach 1:
The patent applies preliminary action by detecting cache hazards before they cause redundant operations. The hazard detection mechanism checks whether a demand fetch address matches a pending prefetch address before the demand fetch is serviced, allowing the system to preemptively prevent redundant memory operations and associated power consumption.
Solution Approach 2:
The patent converts the potentially harmful cache hazard (redundant operations) into a benefit by using the hazard detection information to optimize power consumption. When a hazard is detected, the system can cancel or consolidate the redundant demand fetch, transforming what would be wasted energy into improved power efficiency.
2Measurement precision
If address comparators are continuously powered to detect cache hazards, then cache hazard detection accuracy is maintained, but electrical power consumption increases
Solution Approach 1:
The patent applies dynamics by making the address comparator power state variable rather than static. The comparators are dynamically powered on only when needed for hazard detection (when both prefetch and demand fetch operations are active) and powered off otherwise, allowing the system to maintain detection accuracy when required while minimizing power consumption during normal operation.
Solution Approach 2:
The patent implements periodic action by activating address comparators only during specific time windows when cache hazards are possible (when prefetch operations are pending and demand fetches may occur). This periodic activation pattern maintains hazard detection capability while avoiding continuous power consumption.
3Reliability
If all address comparators are powered to check for cache hazards, then comprehensive hazard detection is achieved, but device complexity and power consumption increase
Solution Approach 1:
The patent applies segmentation by dividing the address comparator functionality into manageable segments that can be independently controlled. Rather than a single monolithic comparator system, the architecture allows selective activation of comparison operations based on specific conditions, reducing overall system complexity while maintaining comprehensive hazard detection coverage.
Data Source
AI summary
Disclosed embodiments provide a technique in which a memory controller determines whether a fetch address is a miss in an L1 cache and, when a miss occurs, allocates a way of the L1 cache, determines whether the allocated way matches a scoreboard entry of pending service requests, and, when such a match is found, determine whether a request address of the matching scoreboard entry matches the fetch address. When the matching scoreboard entry also has a request address matching the fetch address, the scoreboard entry is modified to a demand request.