Branch prediction related Optimizations for Multithreaded Processors

TL;DR

This paper proposes a branch prediction monitoring and feedback mechanism to optimize thread scheduling in multithreaded processors, aiming to reduce resource wastage caused by branch mispredictions.

Contribution

It introduces a novel feedback-based thread scheduling method that adapts to branch prediction behavior to improve resource utilization in multithreaded processors.

Findings

Qualitative comparison of solutions for branch misprediction issues

Identification of phases with high branch misprediction stalls

Potential for improved resource efficiency through feedback mechanisms

Abstract

Major chip manufacturers have all introduced Multithreaded processors. These processors are used for running a variety of workloads. Efficient resource utilization is an important design aspect in such processors. Depending on the workload, mis-speculated execution can severely impact resource utilization and power utilization. In general, compared to a uniprocessor, a multithreaded processor may have better tolerance towards mis-speculation. However there can still be phases where even a multi-threaded processor performance may get impacted by branch induced mis-speculation. In this paper I propose monitoring the branch predictor behavior of various hardware threads running on the multi-threaded processor and use that information as a feedback to the thread arbiter/picker which schedules the next thread to fetch instructions from. If I find that a particular thread is going through a phase where it is consistently mis-predicting its branches and its average branch misprediction stall is above a specific threshold then I temporarily reduce the priority for picking that thread. I do a qualitative comparison of various solutions to the problem of resource inefficiency caused due to mis-speculated branches in multithreaded processors. This work can be extended by doing a quantitative evaluation.