Soft Real-Time Scheduling in Google Earth

Google Earth is a virtual globe that allows users to explore satellite imagery, terrain, 3D buildings, and geo-spatial content. It is available on a wide variety of desktop and mobile platforms, including Windows, Mac OS X, Linux, iOS, and Android. To preserve the sense of fluid motion through a 3D environment, the application must render at 60Hz. In this paper, we discuss the scheduling constraints of this application as a soft real-time scheduling problem where missed deadlines disrupt this motion. We describe a new scheduling implementation that addresses these problems. The diversity of hardware and software platforms on which Google Earth runs makes offline execution time analysis infeasible, so we discuss ways to predict execution time using on line measurement. We provide experimental results comparing different methods for predicting execution time. This new implementation is slated for inclusion in a future release of Google Earth.