Prefetching Circuitry for Memory Address Prediction and Data Pre-alignment
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Solution Overview
Problem
Data processing apparatuses face challenges in improving memory access speed due to the need for frequent loading of data from memory, which can be slowed down by cache misses and misaligned data.
Innovation Solution
The apparatus employs prefetching circuitry to predict memory addresses based on iterative instruction histories, pre-aligns data values to match register formats, and stores these pre-aligned values in a cache for quick retrieval, thereby suppressing unnecessary memory access requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If data is loaded from memory using conventional caching, then memory access speed is improved, but cache misses and misaligned data still cause performance degradation
Solution Approach 1:
The system performs preliminary actions by predicting future memory addresses and pre-loading data into the cache before it is actually needed. The prefetching circuitry analyzes iterative instruction histories to forecast memory access patterns, and the cache is proactively populated with anticipated data, eliminating cache misses before they occur.
Solution Approach 2:
The system implements feedback mechanisms where the prefetching circuitry continuously monitors and analyzes actual memory access patterns and instruction histories. This feedback loop allows the predictor to refine its accuracy over time by learning from real access behavior, improving subsequent predictions and reducing cache misses.
2Loss of time
If data is pre-fetched into cache, then memory access latency is reduced, but data alignment requirements are not met without additional processing
Solution Approach 1:
The system performs preliminary alignment actions by pre-aligning data in the cache according to the predicted register format before the actual load instruction executes. The data pre-alignment circuitry processes the cached data to ensure it is properly formatted and aligned for the target register, eliminating the need for post-fetch alignment operations.
Solution Approach 2:
The system introduces an intermediary data pre-alignment circuitry layer between the cache and the load handling circuitry. This intermediary component receives pre-fetched data, performs alignment transformations to match the predicted register format, and outputs properly aligned data, thereby simplifying the overall data path requirements.
3Productivity
If prefetching is implemented to predict memory addresses, then data availability is improved, but prediction accuracy decreases with complex access patterns
Solution Approach 1:
The system implements dynamic adaptation by adjusting prediction strategies based on the complexity and characteristics of current access patterns. The prefetching circuitry monitors actual access behavior and dynamically modifies its prediction algorithms to handle varying workloads, maintaining high accuracy across diverse and changing memory access patterns.
Solution Approach 2:
The system uses feedback from actual memory access outcomes to continuously refine prediction accuracy. By analyzing whether predictions were correct and measuring access patterns, the system adapts its prediction algorithms in real-time, improving precision even for complex and varying access patterns through iterative learning.
Data Source
AI summary
An apparatus with prefetching capabilities is provided in order to produce predictions of a memory address to be accessed by a load instruction in the future. An additional special cache is provided where pre-aligned data can be stored based on that prediction. When that load instruction is eventually received, the prediction can be confirmed and the pre-aligned data returned and loaded into a register file. In accordance with these techniques, the load instruction does not need to access the memory system nor perform alignment of the data before loading it into the register file. Hence the load instruction is performed faster than when loading data via a memory access. Further precautionary functionalities are also provided to manage the pre-aligned data to avoid the possibility of data corruption after a substantive change occurs to the state of memory.