An efficient optimistic time management algorithm for discrete-event simulation system

Abstract

Time Wrap algorithm is a well-known mechanism of optimistic synchronization in a parallel discrete-event simulation (PDES) system. It offers a run time recovery mechanism that deals with the causality errors. For an efficient use of rollback, the global virtual time (GVT) computation is performed to reclaim the memory, commit the output, detect the termination, and handle the errors. This paper presents a new unacknowledged message list (UML) scheme for an efficient and accurate GVT computation. The proposed UML scheme is based on the assumption that certain variables are accessible by all processors. In addition to GVT computation, the proposed UML scheme provides an effective solution for both simultaneous reporting and transient message problems in the context of synchronous algorithm. To support the proposed UML approach, two algorithms are presented in details, with a proof of its correctness. Empirical evidence from an experimental study of the proposed UML scheme on PHOLD benchmark fully confirms the theoretical outcomes of this paper.

A Scalable GVT Estimation Algorithm for PDES: Using Lower Bound of Event-Bulk-Time

“…Processors use EBs to record the number of events sent and received by LPs, as well as the LVT of each LP and the timestamps of events in transit. GVT computation via the EB approach can avoid message acknowledgement, which is a common solution for the problem of transient event in distributed GVT algorithms [16,17,20,21]. In our algorithm, the size of Event-Bulk is negatively correlated with the accuracy of GVT computation but positively correlated with the performance of GVT computation.…”

“…In GVT algorithms for distributed memory platforms, LPs communicate their LVTs and the timestamps of events in transit with each other by exchanging messages. GVT algorithms have to tackle two problems: the LVT simultaneous reporting problem and the transient message problem [20,21]. The LVT simultaneous reporting problem is that it is difficult to measure LVTs of all LPs running concurrently on different processors (or threads) at the same wall-clock time.…”

“…For example, acknowledging individual messages scheme doubles the number of messages to decrease the performance of simulations. Although some methods, such as acknowledging batches of messages [30] and piggyback acknowledgement [21,24], were devised to reduce the acknowledgement overhead, the acknowledgement scheme becomes complex.…”

A Logical Process Simulation Model for Conservative Distributed Simulation Systems

“…Conservative synchronization is performed using the NMA and its variant techniques. Some recent advancements and interesting results in the optimistic algorithms can be found in [7][8][9][10]. Conservative protocols fundamentally maintain causality in event execution by strictly disallowing the processing of events out of time-stamp order [4].…”

“…The need for message exchange, interoperability, reduced latency, and parallel execution are motivating principles behind dividing a single large simulation into number of events and distributing them into distant nodes in a distrusted network [7]. Each of the above mentioned principles clearly require synchronization to be the least common denominator.…”