Live Webcast 15th Annual Charm++ Workshop

Applications often involve iterative execution of identical or slowly evolving calculations. Such applications require incremental rebalancing to improve load balance across iterations. In this paper, we consider the design and evaluation of two distinct approaches to addressing this challenge: persistence-based load balancing and work stealing. The work to be performed is over decomposed into tasks, enabling automatic rebalancing by the middleware. We present a hierarchical persistence-based rebalancing algorithm that performs localized incremental rebalancing. We also present an active-message-based retentive work stealing algorithm optimized for iterative applications on distributed memory machines. We demonstrate low overheads and high efficiencies on the full NERSC Hopper (146,400 cores) and ALCF Intrepid systems (163,840 cores), and on up to 128,000 cores on OLCF Titan.