Windowed Confirmation Queue for Cache Prefetcher
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Solution Overview
Problem
Current computer processor confirmation queues require large content addressable memory structures with high power consumption and complexity, making them inefficient for managing prefetch distances and reducing cache performance due to increased latency and cache pollution.
Innovation Solution
A cache prefetcher system incorporating a pattern predictor circuit and a windowed confirmation queue to predict and confirm memory addresses, reducing the need for a large CAM structure by maintaining a subset of predicted addresses within a windowed queue, thereby minimizing hardware requirements and improving prefetch accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large CAM structure is used for confirmation queue, then prefetch accuracy is improved, but power consumption and device complexity increase
Solution Approach 1:
The confirmation queue is segmented into multiple smaller queues organized in a tree structure, where each node contains a small CAM structure. This divides the large CAM into manageable segments that can be independently managed and accessed, reducing the power consumption and complexity associated with a single large CAM while maintaining the ability to accurately confirm prefetches.
2Measurement precision
If a large CAM structure is used for confirmation queue, then prefetch accuracy is improved, but device area and complexity increase
Solution Approach 1:
The confirmation queue is segmented into multiple smaller queues organized in a tree structure, where each node contains a small CAM structure. This divides the large CAM into manageable segments that can be independently managed and accessed, reducing the power consumption and complexity associated with a single large CAM while maintaining the ability to accurately confirm prefetches.
Solution Approach 2:
The confirmation queue is reorganized from a single large two-dimensional CAM structure into a three-dimensional tree structure with multiple levels. This dimensional transformation allows the system to achieve the functionality of a large CAM while distributing the hardware resources across multiple levels and nodes, thereby reducing the complexity and area requirements of any single level.
3Productivity
If many incorrect prefetches are issued to cover DRAM access latency, then cache performance is improved, but memory system overload and throughput reduction occur
Solution Approach 1:
The confirmation queue provides immediate feedback on whether each prefetch was accurate or incorrect by comparing the prefetched address against the actual demanded address. This feedback mechanism allows the system to learn from past prefetch outcomes and adjust future prefetching behavior, thereby reducing the number of incorrect prefetches and preventing memory system overload while maintaining high cache performance.
Data Source
AI summary
According to one general aspect, an apparatus may include a cache pre-fetcher configured to predict data to be retrieved from a memory system. The cache pre-fetcher may include a pattern predictor circuit and a confirmation queue circuit. The pattern predictor circuit may be configured to predict a series of memory addresses to be pre-fetched from the memory system. The confirmation queue circuit may be configured to: maintain a windowed confirmation queue of predicted memory addresses, compare a requested memory address against the predicted memory addresses, and, if the requested memory address is included in the predicted memory addresses, indicate that a successful pre-fetch has occurred.