A Framework for Monte-Carlo Tree Search on CPU-FPGA Heterogeneous Platform via on-chip Dynamic Tree Management
Yuan Meng, Rajgopal Kannan, Viktor K. Prasanna · 2023
Monte Carlo Tree Search (MCTS) is a widely used search technique in Artificial Intelligence (AI) applications. MCTS manages a dynamically evolving decision tree (i.e., one whose depth and height evolve at run-time) to guide an AI agent toward an optimal policy. In-tree operations are memory-bound leading to a critical performance bottleneck for large-scale parallel MCTS on general-purpose processors. CPU-FPGA accelerators can alleviate the memory bottleneck of in-tree operations. However, a major challenge for existing FPGA accelerators is the lack of dynamic memory management due to which they cannot efficiently support dynamically evolving MCTS trees. In this work, we address this challenge by proposing an MCTS acceleration framework that (1) incorporates an algorithm-hardware co-optimized accelerator design that supports in-tree operations on dynamically evolving trees without expensive hardware reconfiguration; (2) adopts a hybrid parallel execution model to fully exploit the compute power in a CPU-FPGA heterogeneous system; (3) supports Python-based programming API for easy integration of the proposed accelerator with RL domain-specific bench-marking libraries at run-time. We show that by using our framework, we achieve up to 6.8× speedup and superior scalability of parallel workers than state-of-the-art parallel MCTS on multi-core systems.