Selective Instruction Pipeline Flush Controller for Processor Interrupts
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Solution Overview
Problem
Instruction pipelining in processors faces performance penalties due to structural hazards like branch mispredictions, which increase with pipeline depth and require costly multi-path execution, leading to delays and reduced performance.
Innovation Solution
A selective instruction pipeline flush controller determines if the correct target address is present in the pipeline after a precise interrupt, allowing selective flushing of instructions back to that address, reducing the need for full pipeline refetching and minimizing performance penalties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a deeper instruction pipeline is used to increase frequency scaling and performance, then processor throughput is improved, but the penalty from structural hazards increases
Solution Approach 1:
The patent applies preliminary action by checking whether the target address of a mispredicted branch is already present in the instruction pipeline before initiating a full flush. This advance check allows the system to prepare for potential hazards and take corrective action only when necessary, avoiding unnecessary pipeline stalls and maintaining higher throughput despite deeper pipeline depth.
2Speed
If a deeper instruction pipeline is used, then frequency scaling is improved, but the number of instructions needing refetch after hazard increases
Solution Approach 1:
The patent extracts only the necessary portion of the pipeline for flushing by identifying the specific location where the target address exists and flushing only up to that point. This selective extraction approach minimizes the number of instructions that need to be refetched while still resolving the structural hazard, thereby reducing the loss of instructional work despite operating at higher frequencies with deeper pipelines.
3Productivity
If multi-path execute is implemented to handle branch mispredictions, then performance is maintained, but device complexity increases
Solution Approach 1:
The patent applies partial action by implementing a selective flushing mechanism that activates only when a branch misprediction occurs and the target address is not already in the pipeline. Instead of maintaining all possible execution paths simultaneously (excessive action), the system takes a partial approach by flushing only the necessary instructions, thereby maintaining performance with reduced complexity compared to full multi-path execution.
Data Source
AI summary
Selective flushing of instructions in an instruction pipeline in a processor back to an execution-determined target address in response to a precise interrupt is disclosed. A selective instruction pipeline flush controller determines if a precise interrupt has occurred for an executed instruction in the instruction pipeline. The selective instruction pipeline flush controller determines if an instruction at the correct resolved target address of the instruction that caused the precise interrupt is contained in the instruction pipeline. If so, the selective instruction pipeline flush controller can selectively flush instructions back to the instruction in the pipeline that contains the correct resolved target address to reduce the amount of new instruction fetching. In this manner, as an example, the performance penalty of precise interrupts can be lessened through less instruction refetching and reduced delay in instruction pipeline refilling when the instruction containing the correct target address is already contained in the pipeline.