BZSim: Fast, Large-Scale Microarchitectural Simulation with Detailed Interconnect Modeling

Paper i proceeding, 2024

Modeling of on-chip interconnects in microarchitectural simulations is becoming more important. Chips continue to increase their number of cores, i.e., via 3D stacking and multi-chiplet integration, and their performance is gradually more affected by their network. However, existing simulation alternatives are either too slow for large systems or lack support for modeling interconnects, which is on its own a computationally intensive task. This work offers an open-source solution that integrates an accurate, widely used network simulator into an existing fast, parallel microarchitectural simulator enhanced with a new mechanism to make network modeling lightweight. It is based on the observation that a significant fraction of the network traffic has low contention and on the conjecture that the latency of such traffic can be calculated analytically with good accuracy. The proposed approach offers a mechanism to detect low contention traffic and analytically calculate its latency reducing the overheads of network simulation. In essence, it offers a knob for trading simulation accuracy for speed. This tradeoff is explored by demonstrating 2-4× faster simulations within 3-5% error in normalized IPC and 10-20% in average packet latency. Our simulation setup is an order of magnitude faster than an optimistic gem5 setup with point-to-point interconnects and 3× slower than a ZSim setup without network modeling. Our approach is further used to assess the impact of Networkon-Chip designs on system performance and shows that a 32-core system is on average 1.2× faster when using the current state of the art NoC instead of a baseline NoC.