Branch Mis-prediction Buffer for Zero Penalty Instruction Retrieval
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Solution Overview
Problem
Conventional branch prediction methods suffer from significant time delays and computational penalties due to mis-predictions, as they discard mis-predicted instructions, leading to inefficient retrieval of correct instructions from program memory during subsequent branch mis-predictions.
Innovation Solution
A branch mis-prediction buffer is introduced to store correct instructions that were not predicted during previous mis-predictions, allowing for zero mis-prediction penalty by retrieving them directly from the buffer during subsequent mis-predictions, rather than from program memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If branch prediction is used to reduce time delays, then instruction retrieval speed is improved, but mis-prediction penalties increase computational cycles
Solution Approach 1:
The branch mis-prediction buffer pre-stores instructions that were incorrectly predicted during previous branch mis-predictions. When a mis-prediction occurs, the system checks the buffer first before retrieving from program memory, effectively performing the retrieval action in advance for future mis-predictions of the same branch pattern.
Solution Approach 2:
The system creates a copy of mis-predicted instructions and stores them in a separate buffer structure. This copy mechanism allows the system to quickly retrieve instruction copies from the buffer without accessing the original program memory, eliminating the time penalty associated with re-fetching the same mis-predicted instructions.
2Productivity
If mis-predicted instructions are discarded, then pipeline efficiency is maintained, but computational cycles are wasted retrieving correct instructions from program memory
Solution Approach 1:
Instead of completely discarding mis-predicted instructions, the system recovers valuable information by identifying and storing the correct instructions that were missed during mis-predictions. The buffer recovers these instructions for future use, transforming what would be wasted retrieval cycles into productive pre-cached data.
3Measurement precision
If dynamic branch prediction is used, then prediction accuracy improves for correlated branches, but it provides no benefit for algorithms with no branch correlation
Solution Approach 1:
The branch mis-prediction buffer provides a universal solution that benefits all branch prediction scenarios regardless of algorithm type. Whether the branch predictor is static or dynamic, correlated or uncorrelated, the buffer captures and stores mis-predicted instructions from any source, making the system adaptable to different algorithm characteristics without requiring algorithm-specific optimization.
Data Source
AI summary
A system and method is provided for executing a conditional branch instruction. The system and method may include a branch predictor to predict one or more instructions that depend on the conditional branch instruction and a branch mis-prediction buffer to store correct instructions that were not predicted by the branch predictor during a branch mis-prediction.