Micro-operation Supply Rate Variation for Pipeline Flush Reduction
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Solution Overview
Problem
In data processing, existing technologies face performance issues due to mispredictions in predicting the number of loop iterations, leading to pipeline bubbles and flush operations that incur performance penalties.
Innovation Solution
An apparatus comprising processing circuitry, front-end circuitry, and prediction circuitry that generates predictions of loop iterations, with the front-end circuitry varying the supply rate of micro-operations based on the confidence level of the prediction to minimize pipeline bubbles and flush operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the front end circuitry supplies micro-operations at a high supply rate based on a loop iteration prediction, then processing throughput is improved, but if the prediction is incorrect, flush operations are triggered causing performance penalties
Solution Approach 1:
The front end circuitry dynamically adjusts the supply rate of micro-operations based on the confidence level of the loop iteration prediction. When confidence is high, the supply rate is increased to maximize throughput; when confidence is low, the supply rate is reduced to minimize the impact of potential mispredictions and avoid flush operations. This dynamic adjustment resolves the contradiction by making the system adaptive to prediction reliability.
Solution Approach 2:
The system changes the supply rate parameter according to the prediction confidence level. By varying this parameter based on the reliability of the loop iteration prediction, the system optimizes the balance between throughput and prediction accuracy, allowing high performance when predictions are reliable while minimizing penalties when they are not.
2Measurement precision
If the front end circuitry waits to supply micro-operations until actual loop iterations are resolved, then prediction accuracy is improved, but processing delay increases
Solution Approach 1:
Instead of waiting for complete resolution of actual loop iterations before supplying any micro-operations, the front end circuitry supplies micro-operations partially based on predictions. It provides a supply rate that is excessive when predictions are confident (potentially causing some misprediction overhead) but reduced when confidence is low, thus avoiding excessive delays while maintaining acceptable accuracy.
Solution Approach 2:
The system performs preliminary action by supplying micro-operations based on predictions before the actual loop iterations are fully resolved. This preliminary supply is adjusted according to prediction confidence, allowing the system to start processing early when predictions are reliable while minimizing delays when predictions are uncertain.
3Speed
If the front end circuitry supplies micro-operations for all predicted loop iterations, then processing speed is improved, but energy consumption increases due to processing unnecessary iterations
Solution Approach 1:
The front end circuitry dynamically controls the supply rate of micro-operations based on prediction confidence. When confidence is high, it supplies micro-operations at a higher rate to maximize processing speed. When confidence is low, it reduces the supply rate to avoid processing potentially unnecessary iterations, thus reducing energy consumption while maintaining acceptable processing speed.
Solution Approach 2:
The system changes the supply rate parameter according to prediction confidence levels. This parameter adjustment allows the system to optimize the trade-off between processing speed and energy consumption by supplying micro-operations at appropriate rates based on the reliability of loop iteration predictions.
Data Source
AI summary
Processing circuitry performs processing operations in response to micro-operations. Front end circuitry supplies the micro-operations to be processed by the processing circuitry. Prediction circuitry generates a prediction of a number of loop iterations for which one or more micro-operations per loop iteration are to be supplied by the front end circuitry, where an actual number of loop iterations to be processed by the processing circuitry is resolvable by the processing circuitry based on at least one operand corresponding to a first loop iteration to be processed by the processing circuitry. The front end circuitry varies, based on a level of confidence in the prediction of the number of loop iterations, a supply rate with which the one or more micro-operations for at least a subset of the loop iterations are supplied to the processing circuitry.