Transparent Distributed Cross-State Synchronization in Optimistic Parallel Discrete Event Simulation

Matteo Principe

Abstract:
Parallel Discrete Event Simulation (PDES) is a powerful technique to simulate real world complex models. In fact, by sharing the workload over different machines, thus parallelizing it over different entities it is possible to satisfy the high amount of computational power and resources needed by such a kind of models. Indeed, taking advantage of this sort of organization allows to overcome both the power wall ([Sut05]) and the memory wall ([McK04]), which represent the main aspects limiting the delivery of high performance executions.
In particular, this thesis directly faces the disadvantages given by distributed memory accesses arising between Logical Processes (LPs, which are the main simulation entities representing real world objects evolving over time, [Fuj90]) while synchronizing between each other. In fact, those LPs are continuously communicating and often requesting access to portions of memory owned by
others. This scenario needs the involved (two or more) LPs to synchronize in order to ensure that the requested operation will be correctly reflected in their memory. This could lead of course to a degradation of performance, given the distributed nature of the system on top of which the simulations are executed. The innovative technique presented in this document exploits the new kernel-level facilities in order to detect, manage and optimize the aforementioned situation, which is known as Event Cross State Synchronization (ECS).
Also, an important result reached in this work is represented by the fact that the provided solution is transparent to the final model developer in the sense that the whole job is handled by the underlying run-time environment, leveraging shared-memory accesses of the simulation state by relying on the data-sharing paradigm and executing and deploying in a seamless manner on distributed memory within clusters of multicore machines.
The whole work was developed on top of an open source, optimistic simulation platform provided by the High Performance and Dependable Computing Systems (HPDCS) research group at Sapienza, University of Rome, called ROme OpTimistic Simulator (ROOT-Sim).
The remainder of this thesis is organized as follows. In the first chapter, an overview and an explanation of the main topics of simulation and PDES is presented, focusing in particular on the environment and the choices made in this work. In Chapter 2, an introduction to the programming models of PDES is given, going through what literature proposes. Then, in Chapter 3, the proposed solution is discussed, concentrating on the specific implementation and design choices that were made in order to get the best results. Finally, Chapter 4 shows the experimental data for an assessment of the proposed solution.

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