A Study of Branch Prediction and Fetch Policy on Simultaneous Multithreading Architecture

摘要

In the present computer architecture, speculation execution is the general and effective way to handle the branch problem. The performance improvement from the speculation execution relies on the prediction accuracy. However, the simultaneous multithreading (SMT) architecture that combines hardware features of wide-issue superscalar and multithreaded architecture to issue instructions from multiple threads each cycle may have different prediction behavior. Thus features of SMT architecture and branch prediction are the primary focus of this study. We propose a branch prediction mechanism with biased branch filter and confidence estimator to reduce the competition for branch predictor between thread and classify conditional branches as biased or confident branches. And then fetch unit that plays an important role in the SMT architecture decides which threads to fetch instructions from each cycle according to the information from our proposed branch prediction mechanism.