NetGVT: offloading global virtual time computation to programmable switches

Distributed discrete-event simulation is an essential method for analyzing large-scale models, including weather forecast and network simulations. A distributed simulation often requires synchronizing state among the different parts of the model according to a global virtual time (GVT). However, existing approaches require multiple round-trip times to a server to compute a new GVT value. In this paper, we propose NetGVT, a system that computes GVT using programmable switches, thereby avoiding the round-trip latency of a server-based solution. In particular, our design is concerned with two main constraints of the switch programming model: the limited number of arithmetic and logic operations and the limited memory available on the device. We aggregate computations and unroll them across different pipeline stages in a hierarchical manner to address the former. Then, we adopt compression mechanisms to store a short representation of virtual clocks in the on-chip registers to tackle the memory limitations. We implemented a prototype of NetGVT and evaluated its performance with a synthetic lock-step simulation in a Tofino switch. Our results demonstrate that NetGVT outperforms techniques that do not rely on in-network computing by 40% in terms of distributed simulations completion time.