Published on Fri Jun 25 2021

Branch Prediction as a Reinforcement Learning Problem: Why, How and Case Studies

Anastasios Zouzias, Kleovoulos Kalaitzidis, Boris Grot

Recent years have seen stagnating improvements to branch predictor (BP)efficacy and a dearth of fresh ideas in branch predictor design. This paper argues that looking at BP from the viewpoint of Reinforcement Learning (RL) facilitates systematic reasoning and exploration of BP designs.

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Abstract

Recent years have seen stagnating improvements to branch predictor (BP) efficacy and a dearth of fresh ideas in branch predictor design, calling for fresh thinking in this area. This paper argues that looking at BP from the viewpoint of Reinforcement Learning (RL) facilitates systematic reasoning about, and exploration of, BP designs. We describe how to apply the RL formulation to branch predictors, show that existing predictors can be succinctly expressed in this formulation, and study two RL-based variants of conventional BPs.