Dynamic Flow Scheduling for DNN Training Workloads in Data Centers

Distributed deep learning (DL) training constitutes a significant portion of workloads in modern data centers that are equipped with high computational capacities, such as GPU servers. However, frequent tensor exchanges among workers during distributed deep neural network (DNN) training can result in heavy traffic in the data center network, leading to congestion at server NICs and in the switching network. Unfortunately, none of the existing DL communication libraries support active flow control to optimize tensor transmission performance, instead relying on passive adjustments to the congestion window or sending rate based on packet loss or delay. To address this issue, we propose a flow scheduler per host that dynamically tunes the sending rates of outgoing tensor flows from each server, maximizing network bandwidth utilization and expediting job training progress. Our scheduler comprises two main components: a monitoring module that interacts with state-of-the-art communication libraries supporting parameter server and all-reduce paradigms to track the training progress of DNN jobs, and a congestion control protocol that receives in-network feedback from traversing switches and computes optimized flow sending rates. For data centers where switches are not programmable, we provide a software solution that emulates switch behavior and interacts with the scheduler on servers. Experiments with real-world GPU testbed and trace-driven simulation demonstrate that our scheduler outperforms common rate control protocols and representative learning-based schemes in various settings.