Transformer: a functional-driven cycle-accurate multicore simulator

Full-system simulators are extremely useful in evaluating design alternatives for multicore. However, state-of-the-art multicore simulators either lack good extensibility due to their tightly-coupled design between functional model (FM) and timing model (TM), or cannot guarantee cycle-accuracy. This paper conducts a comprehensive study on factors affecting cycle-accuracy and uncovers several contributing factors ignored before. Based on the study, we propose a loosely-coupled functional-driven full-system simulator for multicore, namely Transformer. To ensure extensibility and cycle-accuracy, Transformer leverages an architecture-independent interface between FM and TM and uses a lightweight scheme to detect and recover from execution divergence between FM and TM. Based on Transformer, a graduate student only needs to write about 180 lines of code and takes about two months to extend an X86 functional model (QEMU) in Transformer. Moreover, the loosely-coupled design also removes the complex interaction between FM and TM and opens the opportunity to parallelize FM and TM to improve performance. Experimental results show that Transformer achieves an average of 8.4% speedup over GEMS while guaranteeing the cycle-accuracy. A further parallelization between FM and TM leads to 35.3% speedup.