Spatial/Temporal Locality-based Load-sharing in Speculative Discrete Event Simulation on Multi-core Machines.

The recent literature has reshuffled the architectural organization of speculative parallel discrete event simulation systems for shared-memory multi-core machines. A core aspect has been the full sharing of the workload at the level of individual simulation events, which enables keeping the rollback incidence minimal. However, making each worker thread continuously switch its execution between events destined to different simulation objects does not favor locality. In this article, we propose a workload-sharing algorithm where the worker threads can have short-term binding with specific simulation objects to favor spatial locality and caching effectiveness. Also, new bindings—carried out when a thread decides to switch its execution to other simulation objects—are based on the timeline according to which the object states have passed through the caching hierarchy. At the same time, our solution still enables the worker threads to focus their activities on the events to be processed whose timestamps are closer to the simulation commit horizon—hence we exploit temporal locality along virtual time and keep the rollback incidence minimal. In our design we exploit lock-free constructs to support scalable thread synchronization while accessing the shared event pool. Furthermore, we exploit a multi-view approach of the event pool content, which additionally favors local accesses to the parts of the event pool that are currently relevant for the thread activity. Our solution has been released as an integration within the USE open source speculative simulation platform available to the community. Furthermore, in this article we report the results of an experimental study that shows the effectiveness of our proposal.