Segmented Store Buffer for Store-to-Load Forwarding
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Solution Overview
Problem
Existing data processing systems face challenges in efficiently managing store operations and load operations due to the need for store-to-load forwarding (STLF) and the trade-off between store buffer capacity and STLF timing.
Innovation Solution
A segmented store buffer is introduced, comprising two types of entries: a first type for immediate STLF and a second type for delayed processing, allowing for optimized STLF timing and increased store buffer capacity without compromising performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the store buffer capacity is increased to improve STLF performance, then the likelihood of pipeline stalls is reduced, but the device complexity and timing constraints worsen
Solution Approach 1:
The store buffer is divided into two distinct types of entries: first type entries for immediate STLF and second type entries for delayed processing. This segmentation allows the system to handle different store operations with appropriate timing strategies, improving overall STLF performance without proportionally increasing complexity. The lookup circuitry is also segmented to handle different entry types differently, optimizing the forwarding process.
Solution Approach 2:
The store buffer implements dynamic processing where the handling of load operations depends on the type of store buffer entry encountered. First type entries enable immediate forwarding, while second type entries trigger delayed processing. This dynamic approach allows the system to adapt its processing timing based on the specific state of store buffer entries, improving productivity without requiring a uniformly complex structure for all entries.
2Productivity
If the store buffer capacity is increased to reduce pipeline stalls, then data processing efficiency improves, but the clock frequency maintenance becomes more difficult
Solution Approach 1:
By segmenting the store buffer into first type and second type entries, the system can process different entries at different times. First type entries are processed immediately to maintain high clock frequencies, while second type entries are handled in delayed processing. This segmentation prevents the entire buffer from bottlenecking the clock frequency while still providing large capacity for reducing pipeline stalls.
Solution Approach 2:
The store buffer performs preliminary classification of entries into first type and second type when store operations are issued. This preliminary action allows the lookup circuitry to quickly determine the appropriate processing path without adding complexity to the critical timing path, thereby maintaining clock frequency while improving overall data processing efficiency through increased buffer capacity.
3Speed
If immediate STLF is performed for all store buffer entries, then the forwarding speed increases, but the device complexity and timing constraints worsen
Solution Approach 1:
The lookup circuitry is segmented to first identify the type of store buffer entry before performing STLF operations. First type entries follow an immediate forwarding path with simpler logic, while second type entries are routed to delayed processing. This segmentation reduces the complexity of the immediate forwarding path while maintaining high forwarding speed for eligible entries.
Solution Approach 2:
Different parts of the store buffer have different qualities: first type entries are optimized for immediate forwarding with simpler lookup requirements, while second type entries are designed for delayed processing with more complex handling. This local quality differentiation allows the lookup circuitry to maintain high speed for the common case (first type entries) without requiring complex logic for all entries, thereby reducing overall device complexity while maintaining forwarding speed where critical.
Data Source
AI summary
An apparatus comprises processing circuitry to issue store operations to store data to a data store and load operations to load data from the data store and a store buffer comprising entries to store entry information corresponding to store operations in advance of the store operations completing. Store buffer lookup circuitry is provided to lookup, in response to a load operation, whether the store buffer contains a corresponding entry corresponding to an older store operation for which target addresses of the load operation and the older store operation satisfy an address comparison condition. The store buffer lookup circuitry is configured to perform store-to-load forwarding in response to the load operation when the corresponding entry is a first type of store buffer entry satisfying a forwarding condition, and delay processing of the load operation when the corresponding entry is a second type of store buffer entry satisfying the forwarding condition.