Overcoming Orchestration Bottlenecks at Exascale: A Decentralized, Policy-Driven Approach for Sim-AI Ensembles

2026-07-13

AI Summary

This work addresses the orchestration bottlenecks faced by ultra-large-scale Sim-AI workflows on leadership-class supercomputers, which arise from task heterogeneity and extreme ensemble sizes. To overcome these challenges, the authors propose EnsembleLauncher, a recursively hierarchical and fully decentralized workflow orchestrator that introduces a decentralized control plane and a programmable scheduling policy interface, thereby surpassing conventional tools in both scalability and scheduling flexibility. Experiments on the Aurora supercomputer demonstrate that EnsembleLauncher can efficiently schedule system-wide resources to support up to 8 million serial tasks, achieving more than a fourfold performance improvement over state-of-the-art alternatives. Furthermore, it significantly enhances resource utilization for workloads with high task variance and active learning pipelines.

Abstract

Scientific computing is increasingly shifting from monolithic applications to coupled simulation-AI workflows composed of highly heterogeneous tasks with diverse hardware, scale, and runtime requirements. As these workflows scale to leadership-class systems, the resulting extreme ensemble sizes and task variability can create orchestration bottlenecks. System-level schedulers are often configured for limited throughput, while workflow tools face scalability issues due to rigid control-plane topologies and static scheduling heuristics. We introduce EnsembleLauncher, a recursively hierarchical workflow orchestrator for exascale systems, featuring a fully decentralized control plane and a programmable scheduling policy interface. On the Aurora supercomputer, EnsembleLauncher successfully scales to the entire machine with up to eight million serial tasks, outperforming state-of-the-art tools by more than four times. Additionally, we implement a programmable scheduling interface and demonstrate a significant impact of scheduling policies on resource utilization for high-variance ensembles and active learning pipelines representative of modern coupled simulation-AI workflows.

Problem

• orchestration bottlenecks
• exascale
• simulation-AI workflows
• task heterogeneity
• scalability

Innovation

• decentralized orchestration
• programmable scheduling
• exascale workflows
• simulation-AI ensembles
• hierarchical workflow management