Load Instruction Segmentation for Memory Disambiguation
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Solution Overview
Problem
Modern microprocessors face inefficiencies in predicting and processing memory access dependencies, leading to pipeline stalls due to cache misses and data dependencies, particularly in cases where data locality is low, resulting in increased processor cycles and latency.
Innovation Solution
The implementation of control logic that determines whether a load instruction is a stack access or a non-stack access, allowing for targeted prediction and processing, where stack accesses are treated as dependent on older store instructions and blocked from the data cache, while non-stack accesses are treated as independent and allowed to access the data cache, thereby optimizing data forwarding and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all load instructions access both data cache and store buffer in parallel, then data correctness is maintained, but processing efficiency decreases due to unnecessary accesses and increased complexity
Solution Approach 1:
The patent segments load instructions into two distinct types: stack accesses and non-stack accesses. This segmentation allows each type to be processed differently - stack accesses are directed to the store buffer while non-stack accesses are directed to the data cache, eliminating unnecessary parallel accesses and improving processing efficiency while maintaining data correctness through type-specific handling
Solution Approach 2:
The patent applies local quality by treating different load instructions differently based on their characteristics. Stack accesses (which have high spatial and temporal locality) receive specialized handling with store buffer access, while non-stack accesses use standard data cache access. This localized differentiation optimizes performance for each access pattern without compromising overall system reliability
2Reliability
If data forwarding is applied to all load instructions, then data dependency resolution is improved, but incorrect data may be forwarded from store buffer for non-stack accesses
Solution Approach 1:
The patent segments load instructions into stack accesses and non-stack accesses, applying data forwarding only to stack accesses which have high spatial and temporal locality and are likely to benefit from store buffer forwarding. Non-stack accesses are excluded from store buffer forwarding, preventing incorrect data from being forwarded while maintaining correct dependency resolution for the subset of loads that actually benefit from the optimization
Solution Approach 2:
The patent applies local quality by selectively enabling data forwarding only for stack accesses that have the necessary locality characteristics. This localized application prevents incorrect data forwarding to non-stack accesses while maintaining proper data dependency resolution for stack accesses, thereby eliminating the harmful effect of incorrect data forwarding without losing the benefit for applicable instructions
3Productivity
If stack accesses are blocked from data cache and directed to store buffer, then data forwarding efficiency is improved, but access latency may increase for stack operations
Solution Approach 1:
The patent segments load instructions into stack accesses and non-stack accesses, directing stack accesses to the store buffer where data forwarding can occur. This segmentation improves data forwarding efficiency by ensuring that instructions with high spatial and temporal locality receive optimized handling, while the store buffer's ability to provide fast data for dependent instructions compensates for any additional latency
Solution Approach 2:
The patent enables continuity of useful action by using the store buffer to provide fast data forwarding for stack accesses. Even though stack accesses are blocked from the data cache, the store buffer continuously provides data to dependent instructions, maintaining productive action and reducing the impact of access latency through efficient data reuse and forwarding
Data Source
AI summary
A system and method for efficient predicting and processing of memory access dependencies. A computing system includes control logic that marks a detected load instruction as a first type responsive to predicting the load instruction has high locality and is a candidate for store-to-load (STL) data forwarding. The control logic marks the detected load instruction as a second type responsive to predicting the load instruction has low locality and is not a candidate for STL data forwarding. The control logic processes a load instruction marked as the first type as if the load instruction is dependent on an older store operation. The control logic processes a load instruction marked as the second type as if the load instruction is independent on any older store operation.