Investigating the Effects of Trees and Butterfly Barriers on the Performance of Optimistic GVT Algorithm

The final publication is available at www.springerlink.comThere is two approaches for handling timing constraints in a heterogeneous network; conservatives and optimistic algorithms. In optimistic algorithms, time constraints are allowed to be violated with the help of a time wrap algorithm. Global Virtue Time (GVT) is a necessary mechanism for implementing time wrap algorithm. Mattern [2] has introduced an algorithm for GVT based computation using a ring structure. which showed high latency. The performance of this optimistic algorithm is optimal since it gives accurate GVT approximation. However, this accurate GVT approximation comes at the expense of high GVT latency. Since this resultant GVT latency is not only high but may vary, the multiple processors involve in communication remain idle during that period of time. Consequently, the overall throughput of a parallel and distributed simulation system degrades significantly In this paper, we discuss the potential use of trees and (or) butterflies structures instead of the ring structure. We present our analysis to show the effect of these new mechanisms on the latency of the system.http://link.springer.com/chapter/10.1007%2F978-90-481-3660-5_7

Gerenciamento descentralizado de tempo virtual global em simula??o distribu?da

A distributed simulation model can support the cooperation between synchronous and asynchronous components. When components are distributed, additional controls are needed to maintain synchronization between them, and this can be done through the concept of virtual time. Each component has a local virtual time (LVT) defined by the occurrence of events. As a way to keep the synchronization of events between components, a time known by all is necessary, called global virtual time (GVT). The GVT can be defined as the lowest timestamp between messages in transit and the LVTs of the components. In the conservative simulation, the GVT defines a state of progress, preventing events whose time is less than the GVT can be executed. In this way, violations can be avoided. The management of GVT can be done in a centralized or decentralized way. The first approach defines a component as a GVT manager, which receives control information from the participants of the simulation and calculates the global time based on them. This form of management makes control dependent on the central process, which can impose some obstacles. An example of this is the existence of the single point of failure. In the difficulty of communication with the controller process, the GVT calculation can be compromised. The second approach works in a decentralized manner, allowing all components to participate in the global time estimation. The distribution over the GVT control requires additional structures that allow the components to keep records on the simulation participants in order to be able to estimate the global simulation time based on the available local information. This work presents a decentralized strategy for the GVT calculation, based on related solutions, allowing a distribution of the control message load.Um modelo de simula??o distribu?da pode suportar a coopera??o entre componentes s?ncronos e ass?ncronos. Quando os componentes s?o distribu?dos, controles adicionais s?o necess?rios para manter a sincroniza??o entre eles, e isto pode ser feito atrav?s do conceito de tempo virtual. Nesta ideia, cada componente possui um tempo virtual local (LVT) definido pela ocorr?ncia dos eventos. Como forma de manter o sincronismo dos eventos entre os componentes, ? necess?rio um tempo conhecido por todos, denominado de tempo virtual global (GVT). Esse tempo pode ser definido como: o menor timestamp entre as mensagens em tr?nsito e os LVTs dos componentes. Na simula??o s?ncrona, o GVT define um estado de progresso, impedindo que os eventos cujo o tempo seja menor que o GVT possam ser executados, para que viola??es de tempo sejam evitadas. O gerenciamento do GVT pode ser feito de forma centralizada ou descentralizada. A primeira abordagem define um componente como gerenciador de GVT, que recebe informa??es de controle dos participantes da simula??o e calcula o tempo global baseado nelas. Essa forma de gerenciamento torna o controle dependente do processo central, o que pode impor alguns obst?culos, tais como: a exist?ncia do ponto ?nico de falha, isto ?, na dificuldade de comunica??o com o processo controlador, o c?lculo de GVT pode ficar comprometido. A segunda abordagem trabalha de forma descentralizada, permitindo que todos os componentes participem da estimativa do tempo global. A distribui??o sobre o controle de GVT requer estruturas adicionais que permitam aos componentes manter registros sobre os participantes da simula??o, a fim de conseguir estimar o tempo global de simula??o baseado nas informa??es locais dispon?veis. Este trabalho apresenta uma estrat?gia descentralizada para o c?lculo de GVT, a partir de solu??es correlatas, permitindo uma distribui??o da carga de controle