TACOS: Topology-Aware Collective Algorithm Synthesizer for Distributed Machine Learning

The surge of artificial intelligence, specifically large language models, has led to a rapid advent towards the development of large-scale machine learning training clusters. Collective communications within these clusters tend to be heavily bandwidth-bound, necessitating techniques to optimally utilize the available network bandwidth. This puts the routing algorithm for the collective at the forefront of determining the performance. Unfortunately, communication libraries used in distributed machine learning today are limited by a fixed set of routing algorithms. This constraints collective performance within the domain of next-generation training clusters that employ intricate, heterogeneous, and asymmetric, large-scale topologies. Further, the emergence of irregular topologies attributed to runtime phenomena such as device failures serves to compound the complexity of the challenge. To this end, this paper introduces TACOS, an automated synthesizer that generates topology-aware collective algorithms for common distributed machine learning collectives across arbitrary input network topologies. TACOS was able to synthesize All-Reduce algorithm for a heterogeneous 512-NPU system in just 6.09 minutes while achieving performance improvement up to 4.27x over state-of-the-art prior work. TACOS exhibits high scalability, with synthesis time scaling quadratically with the number of NPUs. In contrast to prior works' NP-hard approaches, TACOS with 40K NPUs completes in 2.52 hours.