Vidi: Record Replay for Reconfigurable Hardware

Developers are turning to heterogeneous computing devices, such as Field Programmable Gate Arrays (FPGAs), to accelerate data center and cloud computing workloads. FPGAs enable rapid prototyping and should facilitate an agile software-like development workflow to fix correctness bugs, performance issues, and security vulnerabilities. Unfortunately, hardware development still does not have a vast ecosystem of tools needed to support the agile hardware development vision. The capability to record and replay FPGA executions would constitute a key building block that will inspire the development of many tools, similar to what record/replay did for software. However, building a practical record/replay tool for FPGA is challenging; existing approaches either record too much or too little information and cannot support real-world executions. In this paper, we present VIDI, the first record/replay system for real-world FPGA applications running on hardware. VIDI is based on the observation that widely-used communication protocols have well-defined input/output transactions to hide cycle-specific information from developers, which enables a more efficient design than heavyweight cycle-accurate record/replay approaches. VIDI proposes (1) the transaction determinism insight to track and enforce only necessary orderings of transaction events across record and replay, and (2) the coarse-grained input recording mechanism to record transaction-level information. We evaluate VIDI on Amazon EC2 F1 instances with 10 applications and two use cases (debugging, testing) and find that it incurs on average low performance slowdown (1.98%) and resource overhead (5.48%), making it practical for real-world deployments.