Recent years have demonstrated the potential of deep multi-agent reinforcement
learning (MARL) to train groups of AI agents that can collaborate to solve complex
tasks – for instance, AlphaStar achieved professional-level performance in the
Starcraft II video game, and OpenAI Five defeated the world champion in Dota2.
These successes, however, were powered by huge swaths of computational resources;
tens of thousands of CPUs, hundreds of GPUs, and even TPUs were used to collect and train on
a large volume of data. This has motivated the academic MARL community to develop
MARL methods which train more efficiently.
DeepMind’s AlphaStar attained professional level performance in StarCraft II, but required enormous amounts of
computational power to train.
Research in developing more efficient and effective MARL algorithms has focused on off-policy methods – which store and re-use data for multiple policy updates – rather than on-policy algorithms, which use newly collected training data before each update to the agents’ policies. This is largely due to the common belief that off-policy algorithms are much more sample-efficient than on-policy methods.
In this post, we outline our recent publication in which we re-examine many of these assumptions about on-policy algorithms. In particular, we analyze the performance of PPO, a popular single-agent on-policy RL algorithm, and demonstrate that with several simple modifications, PPO achieves strong performance in 3 popular MARL benchmarks while exhibiting a similar sample efficiency to popular off-policy algorithms in the majority of scenarios. We study the impact of these modifications through ablation studies and suggest concrete implementation and tuning practices which are critical for strong performance. We refer to PPO with these modifications as Multi-Agent PPO (MAPPO).