Cross-layer resource control and scheduling for improving interactivity in Android

摘要

Android smartphones are often reported to suffer from sluggish user interactions due to poor interactivity. This is partly because Android and its task scheduler, the completely fair scheduler (CFS), may incur perceptibly long response time to user-interactive tasks. Particularly, the Android framework cannot systemically favor user-interactive tasks over other background tasks since it does not distinguish between them. Furthermore, user-interactive tasks can suffer from high dispatch latency due to the non-preemptive nature of CFS. To address these problems, this paper presents framework-assisted task characterization and virtual time-based CFS. The former is a cross-layer resource control mechanism between the Android framework and the underlying Linux kernel. It identifies user-interactive tasks at the framework-level, by using the notion of a user-interactive task chain. It then enables the kernel scheduler to selectively promote the priorities of worker tasks appearing in the task chain to reduce the preemption latency. The latter is a cross-layer refinement of CFS in terms of interactivity. It allows a task to be preempted at every predefined period. It also adjusts the virtual runtimes of the identified user-interactive tasks to ensure that they are always scheduled prior to the other tasks in the run-queue when they wake up. As a result, the dispatch latency of a user-interactive task is reduced to a small value. We have implemented our approach into Android 4.1.2 running with Linux kernel 3.0.31. Experimental results show that the response time of a user interaction is reduced by up to 77.35% while incurring only negligible overhead. Copyright (C) 2014 John Wiley & Sons, Ltd.