EvLag: A Tool for Monitoring and Lagging Linux Input Devices

Understanding the effects of latency on interaction is important for building software, such as computer games, that perform well over a range of system configurations. Unfortunately, user studies evaluating latency must each write their own code to add latency to user input and, even worse, must limit themselves to open source applications. To address these shortcomings, this paper presents EvLag, a tool for adding latency to user input devices in Linux. EvLag provides a custom amount of latency for each device regardless of the application being run, enabling user studies for systems and software that cannot be modified (e.g., commercial games). Evaluation shows EvLag has low overhead and accurately adds the expected amount of latency to user input. In addition, EvLag can log user input events for post study analysis with several utilities provided to facilitate output event parsing.