Discrete Event Execution with One-Sided and Two-Sided GVT Algorithms on 216,000 Processor Cores

Abstract

Global Virtual Time (GVT) computation is a key determinant of the efficiency and runtime dynamics of Parallel Discrete Event Simulations (PDES), especially on large-scale parallel platforms. Here, three execution modes of a generalized GVT computation algorithm are studied on high-performance parallel computing systems: (1) a synchronous GVT algorithm that affords ease of implementation, (2) an asynchronous GVT algorithm that is more complex to implement but can relieve blocking latencies, and (3) a variant of the asynchronous GVT algorithm to exploit one-sided communication in extant supercomputing platforms. Performance results are presented of implementations of these algorithms on up to 216,000 cores of a Cray XT5 system, exercised on a range of parameters: optimistic and conservative synchronization, fine- to medium-grained event computation, synthetic and nonsynthetic applications, and different lookahead values. Detailed PDES-specific runtime metrics are presented to further the understanding of tightly coupled discrete event dynamics on massively parallel platforms.