In Situ Workflows at Exascale: System Software to the Rescue.

Implementing an in situ workflow involves several challenges related to data placement, task scheduling, efficient communications, scalability, and reliability. Most of the current implementations provide reasonably performant solutions to these issues by focusing on high-performance communications and low-overhead execution models at the cost of reliability and flexibility. One of the key design choices in such infrastructures is between providing a single-program, integrated environment or a multiple-program, connected environment, both solutions having their own strengths and weaknesses. While these approaches might be appropriate for current production systems, the expected characteristics of exascale machines will shift current priorities. After a survey of the trade-offs and challenges of integrated and connected in situ workflow solutions available today, we discuss in this paper how exascale systems will impact those designs. In particular, we identify missing features of current system-level software required for the evolution of in situ workflows toward exascale and how system software innovations from the Argo Exascale Computing Project can help address those challenges.