Speculative Cache Write Logic Eliminates Store Buffer
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Solution Overview
Problem
Conventional cache designs incur inefficiencies due to the need for a store buffer, which increases circuit complexity, power consumption, and latency, leading to sub-optimal system performance when handling store and read operations sequentially.
Innovation Solution
Implementing a speculative cache modification design that allows a cache line to be written speculatively before the store instruction retires from the pipeline, with cache line validation logic to determine validity and invalidate if necessary, eliminating the need for a store buffer and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a store buffer is used to enable reading of store instructions before cache write completion, then instruction throughput is improved, but circuit complexity increases due to additional components like address comparators, data buffering space, and multiplexors
Solution Approach 1:
The patent extracts and removes the store buffer component from the cache system, replacing it with a simplified mechanism that achieves the same functional goal of enabling read operations without requiring complex buffering infrastructure. This eliminates address comparators, data buffering space, and multiplexors while maintaining instruction throughput.
Solution Approach 2:
The patent implements preliminary action by allowing read operations to proceed speculatively before store write completion is confirmed. The system performs read operations in advance based on predicted outcomes, and only validates or rolls back if the store operation ultimately fails, thereby eliminating the need for complex store buffer mechanisms.
2Reliability
If a store buffer is implemented to hold data until store retirement, then data integrity is maintained, but power consumption increases due to additional circuit components
Solution Approach 1:
The patent removes the store buffer component that consumes power, replacing it with a validation mechanism that only activates when needed. This eliminates the continuous power consumption associated with maintaining address comparators, data buffering space, and multiplexors while preserving data integrity through selective validation.
Solution Approach 2:
The patent employs a disposable validation approach where cache lines are marked as potentially invalid temporarily, and validation is performed only when needed. This avoids the continuous power consumption of permanent store buffer structures while maintaining data integrity through on-demand validation.
3Reliability
If data is directed to store buffer first, then cache write occurs after store retirement, but this introduces multiple cycle delays before data becomes available for read operations
Solution Approach 1:
The patent performs read operations preliminarily and speculatively before store retirement is confirmed, rather than waiting for store buffer completion. This allows the system to proceed with read operations in advance based on predictions, significantly reducing the multi-cycle delays inherent in conventional store buffer approaches.
Solution Approach 2:
The patent inverts the conventional sequence by allowing read operations to occur before store write completion is confirmed, rather than waiting for store buffer operations to finish. This reversal of the traditional store-then-read sequence eliminates multiple cycle delays while maintaining data integrity through validation mechanisms.
4Reliability
If store buffer is used to manage cache writes, then cache consistency is maintained, but the area occupied on integrated circuit increases
Solution Approach 1:
The patent extracts and removes the store buffer from the integrated circuit design, eliminating the need for address comparators, data buffering space, and multiplexors that occupy valuable chip area. Cache consistency is maintained through a simplified validation mechanism that uses minimal circuit resources.
Solution Approach 2:
The patent uses a validation copy mechanism where cache line validity is tracked through metadata or status bits rather than requiring physical duplication of data in store buffers. This maintains cache consistency information using minimal area while avoiding the space-intensive store buffer architecture.
Data Source
AI summary
In accordance with embodiments disclosed herein, there are provided methods, systems, mechanisms, techniques, and apparatuses for implementing a speculative cache modification design. For example, in one embodiment, such means may include an integrated circuit having a data bus; a cache communicably interfaced with the data bus; a pipeline communicably interfaced with the data bus, in which the pipeline is to receive a store instruction corresponding to a cache line to be written to cache; caching logic to perform a speculative cache write of the cache line into the cache before the store instruction retires from the pipeline; and cache line validation logic to determine if the cache line written into the cache is valid or invalid, in which the cache line validation logic is to invalidate the cache line speculatively written into the cache when determined invalid and further in which the store instruction is allowed to retire from the pipeline when the cache line is determined to be valid.