Realm: An event-based low-level runtime for distributed memory architectures

We present Realm, an event-based runtime system for het-erogeneous, distributed memory machines. Realm is fully asynchronous: all runtime actions are non-blocking. Realm supports spawning computations, moving data, and reser-vations, a novel synchronization primitive. Asynchrony is exposed via a light-weight event system capable of operat-ing without central management. We describe an implementation of Realm that relies on a novel generational event data structure for efficiently han-dling large numbers of events in a distributed address space. Microbenchmark experiments show our implementation of Realm approaches the underlying hardware performance lim-its. We measure the performance of three real-world ap-plications on the Keeneland supercomputer. Our results demonstrate that Realm confers considerable latency hid-ing to clients, attaining significant speedups over traditional bulk-synchronous and independently optimized MPI codes