Supporting dynamic QoS in Linux

This work is an application of the variable-rate execution (VRE) model in Linux to support dynamic quality of service (QoS). Based on conventional time-sharing scheduling algorithms, Linux does not adequately support QoS requirements. The VRE scheduler can assign a specified execution rate to any application, and dynamically adjust the execution rate during runtime. Rate controller components are introduced to adjust a task's execution rate based on predefined rules and runtime feedbacks, such as the suspension time, the queue length, and so on. A significant feature of this work is its ability to support legacy applications at the binary level. On conventional operating systems, millions of applications have been built under time-sharing schedulers, which we call legacy applications. Under the VRE model, a legacy application can obtain a guaranteed variable execution rate. We also designed a simple default rate controller for legacy multimedia applications. The Linux kernel was slightly modified in our implementation to achieve reconfigurability. Both the VRE scheduler and the default rate controller are implemented as Linux loadable modules, which can be dynamically loaded into the kernel to replace the Linux scheduler or change the behavior of the scheduler. We provide a set of interfaces for users to design and use their own schedulers and rate controllers.