ORCHESTRA: An asynchronous wait-free distributed GVT algorithm

Taking advantage of computing capabilities offered by modern parallel and distributed architectures is fundamental to run large-scale simulation models based on the Parallel Discrete Event Simulation (PDES) paradigm. By relying on this computing organization, it is possible to effectively overcome both the power and the memory wall, which are core limiting aspects to deliver high-performance simulations. This is even more the case when relying on the speculative Time Warp synchronization protocol, which could be particularly memory greedy. At the same time, some form of coordination, such as the computation of the Global Virtual Time (GVT), is required by Time Warp Systems. These coordination points could easily become the bottleneck of large-scale simulations, hindering an efficient exploitation of the computing power offered by large supercomputing facilities. In this paper we present ORCHESTRA, a coordination algorithm which is both wait-free and asynchronous. The nature of this algorithm allows any computing node to carry on simulation activities while the global agreement is reached, thus offering an effective building block to achieve scalable PDES. We claim that the general organization of ORCHESTRA could be adopted by different high-performance computing applications, thus paving the way to a more effective usage of modern computing infrastructures.