Load-Store Unit Dual Tag Arrays and Arbitration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In modern processors, parallel execution of load-store unit operations can lead to cache tag conflicts, causing incorrect execution results due to multiple pipelines accessing the same cache tags, which existing technologies struggle to handle effectively.
Innovation Solution
Implementing a dual pipeline load-store unit with dual tag arrays, where each pipeline performs non-overlapping subsets of operations and control circuitry ensures synchronization and arbitration to allow only one pipeline to write to a tag array per cycle, preventing conflicts and enabling parallel execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple pipelines access the same cache tag array in parallel, then processor throughput is improved, but tag write conflicts occur causing incorrect execution results
Solution Approach 1:
The patent divides the single tag array into multiple separate tag arrays, with each pipeline having its own dedicated tag array. This segmentation eliminates write conflicts between pipelines while maintaining parallel access capability, resolving the contradiction between throughput and execution accuracy.
Solution Approach 2:
The patent introduces an arbitration mechanism as an intermediary that manages access to shared resources between multiple pipelines. The arbitration logic mediates tag array access conflicts and coordinates pipeline operations to prevent incorrect execution while maintaining parallel processing efficiency.
2Reliability
If dual tag arrays are implemented for parallel pipelines, then write conflicts are prevented, but hardware area and power consumption increase
Solution Approach 1:
The patent merges the functionality of multiple tag arrays into a single unified tag array structure that supports parallel access through arbitration. This combining approach maintains conflict-free operation while reducing the total hardware area compared to fully separate tag arrays for each pipeline.
Solution Approach 2:
The patent implements dynamic arbitration that activates only when conflicts are detected, allowing the system to operate efficiently with reduced overhead. The arbitration mechanism dynamically manages access based on actual pipeline needs rather than requiring dedicated arrays for all pipelines simultaneously.
3Productivity
If speculative execution is used to overcome control dependencies, then instruction throughput increases, but misprediction recovery requires replays that reduce performance
Solution Approach 1:
The patent segments the execution pipeline into multiple independent pipelines with separate tag arrays, allowing speculative execution to proceed in parallel without interfering with other pipeline operations. This reduces the impact of misprediction replays on overall throughput by isolating replay operations to specific pipeline segments.
Data Source
AI summary
Techniques are disclosed relating to a processor load-store unit. In some embodiments, the load-store unit is configured to execute load/store instructions in parallel using first and second pipelines and first and second tag memory arrays. In tag write conflict situations, the load-store unit may arbitrate between the first and second pipelines to ensure the first and second tag memory array contents remain identical. In some embodiments, a data cache tag replay scheme is utilized. In some embodiments, executing load/store instructions in parallel with fills, probes, and store-updates, using separate but identical tag memory arrays, may advantageously improve performance.