gem5-SALAM: A System Architecture for LLVM-based Accelerator Modeling

Samuel Rogers, Joshua Slycord, Mohammadreza Baharani, Hamed Tabkhi

Abstract: With the prevalence of hardware accelerators as an integral part of the modern systems on chip (SoCs), the ability to quickly and accurately model accelerators within the system it operates is critical. This paper presents gem5-SALAM as a novel system architecture for LLVM-based modeling and simulation of custom hardware accelerators integrated into the gem5 framework. gem5-SALAM overcomes the inherent limitations of state-of-the-art trace-based pre-register-transfer level (RTL) simulators by offering a truly "execute-in-execute" LLVM-based model. It enables scalable modeling of multiple dynamically interacting accelerators with full-system simulation support. To create sustainable long-term expansion compatible with the gem5 system framework, gem5-SALAM offers a general-purpose and modular communication interface and memory hierarchy integrated into the gem5 ecosystem which streamlines designing and modeling accelerators for new and emerging applications. Validation on the MachSuite [17] benchmarks present a timing estimation error of less than 1% against Vivado High-Level Synthesis (HLS) tool. Results also show less than a 4% area and power estimation error against Synopsys Design Compiler. Additionally, system validation against implementations on a Ultrascale+ ZCU102 shows an average end-to-end timing error of less than 2%. Lastly, this paper presents the capabilities of gem5-SALAM in cycle-level profiling and full system design space exploration of accelerator-rich systems.