Improving Interactivity via VT-CFS and Framework-Assisted Task Characterization for Linux/Android Smartphones

Android smart phones are often reported to suffer from sluggish user interactions due to poor interactivity. This is because the Linux kernel may incur perceptibly long response time to user interactive tasks. Particularly, the completely fair scheduler (CFS) of Linux cannot systematically favor a user interactive task over background tasks since it fails to effectively distinguish between them. Even if a user interactive task is successfully identified, such a task can suffer from a high scheduling latency due to the non-preemptive nature of CFS. This paper presents a framework-assisted task characterization and virtual runtime-based CFS (VT-CFS) to address these problems. The former is a cooperative mechanism between the Android application framework and the kernel. It identifies a user interactive task at the framework level and then enables the task scheduler to selectively promote the priority of the identified task at the kernel level. VT-CFS is an extension of the CFS. It allows a task to be preempted at any preemption tick so that the scheduling latency of a user interactive task is bounded by the tick interval. We have implemented our approach into Android 2.2 running with Linux kernel 2.6.32. Experimental results show that the response time of a user interactive task is reduced by up to 31.4% while incurring only 0.9% more run-time overhead than the legacy system.