Branch prediction: Why CPUs can't wait?
7 days ago
- #Branch Prediction
- #Performance
- #CPU Optimization
- Branch prediction is crucial for CPU performance, allowing parallel execution of instructions by predicting the next steps.
- Modern CPUs use instruction pipelining to process multiple stages of different instructions simultaneously, improving efficiency.
- Branch misprediction occurs when the CPU incorrectly guesses the path of a conditional jump, leading to pipeline flushes and performance penalties.
- The cost of branch misprediction is significant, with modern CPUs experiencing a penalty of around 5ns per misprediction.
- Sorted data leads to predictable branch patterns, enhancing CPU prediction accuracy and performance.
- Random data disrupts branch predictability, causing frequent mispredictions and slower execution times.
- An example with e-commerce data showed a 60% performance difference between sorted and randomly ordered products due to branch prediction effects.
- Without branch prediction, CPUs would stall frequently, waiting for branch resolutions, drastically reducing performance.
- Optimizing data organization (e.g., sorting) can significantly improve branch prediction accuracy and overall program speed.
- Key strategies include processing sorted data, batching similar operations, and minimizing unpredictable conditional logic in critical paths.