Prefetching Circuitry Stride Refinement for Unpredictable Memory Access
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Solution Overview
Problem
Existing data processing systems face inefficiencies due to the time-consuming nature of memory access instructions, particularly when memory access patterns are unpredictable or complicated, leading to delays in processing circuitry operations.
Innovation Solution
The implementation of prefetching circuitry that refines stride lengths based on differences between memory access instructions, using factors to adjust the stride length and maintain confidence values, allowing for effective prefetching even in non-sequential or random access patterns, thereby improving processing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If prefetching is performed based on predicted memory addresses, then processing efficiency is improved, but the system fails when memory access patterns are unpredictable or complicated
Solution Approach 1:
The stride length is made dynamic rather than static. The system initially uses a coarse stride length for prefetching, then refines it based on actual memory access patterns observed during execution. This allows the prefetching mechanism to adapt to both sequential and non-sequential access patterns, resolving the contradiction between maintaining high productivity and handling unpredictable access patterns.
Solution Approach 2:
The system implements feedback by monitoring actual memory access addresses and comparing them with predicted addresses. Based on this feedback, the stride length is refined to better match the actual access pattern. This feedback mechanism enables the system to maintain high processing efficiency even when access patterns are initially unpredictable.
2Ease of manufacture
If a fixed stride length is used for prefetching, then implementation is simple, but accuracy deteriorates when access patterns vary
Solution Approach 1:
The stride length determination process is segmented into two distinct phases: an initial phase using a coarse (simple) stride length for quick implementation, and a refinement phase that adjusts the stride length based on observed access patterns. This segmentation allows the system to maintain implementation simplicity while improving stride length accuracy when needed.
Solution Approach 2:
The system performs preliminary prefetching using a coarse stride length before refinement occurs. This preliminary action ensures that the system can operate with simple implementation from the start, while subsequent refinement improves accuracy without compromising the initial functionality.
3Measurement precision
If prefetching assumes sequential access patterns, then prediction is accurate for arrays, but it fails for random or short-lived thread accesses
Solution Approach 1:
The system transitions from assuming a fixed sequential access pattern to dynamically adapting the stride length based on observed access behavior. This allows accurate prediction for sequential array accesses while also handling random or short-lived thread accesses by refining the stride length to match actual patterns.
Solution Approach 2:
The system changes the stride length parameter based on observed memory access patterns. For sequential array accesses, the stride length remains consistent with the array structure. For random or short-lived accesses, the stride length is refined to match the observed pattern, thereby maintaining prediction accuracy across diverse access patterns.
Data Source
AI summary
A data processing device includes processing circuitry 20 for executing a first memory access instruction to a first address of a memory device 40 and a second memory access instruction to a second address of the memory device 40, the first address being different from the second address. The data processing device also includes prefetching circuitry 30 for prefetching data from the memory device 40 based on a stride length 70 and instruction analysis circuitry 50 for determining a difference between the first address and the second address. Stride refining circuitry 60 is also provided to refine the stride length based on factors of the stride length and factors of the difference calculated by the instruction analysis circuitry 50.