Research On Scheduling Technology Of Microkernel

The development of computer technology is becoming faster and faster in the 21st century. Microkernel technology, as an important research direction of operating system, is getting more and more concern by the researchers.This paper introduces the concepts of microkernel, describes the history of microkernel-based operating systems, the structure and technology. We focus on the design of the L4 microkernel framework and technical characteristics, and go into the details of its three major components, thread management, address space management and IPC mechanisms. Based on the above study, this paper studies the microkernel's scheduling strategy and analyzes its deficiencies. Scheduling strategy plays an important role in the operating system to provide users with a wealth of real-time scheduling strategy. However, in order to keep the size small enough, microkernel implemented only the most basic scheduling policies. Users need to implement its scheduling strategy in the user level to achieve their goals. On the other hand, users can only use limited interface, which is provided by the microkernel, to access scheduling information. But frequently invoking these calls will affect the performance of the system.Based on the above research, this paper has proposed a solution. The main work of this paper includes the following points:First, this paper designs and implements a two-layer scheduling framework, which is constructed on L4 microkernel. Through this framework, user-level scheduler can control the communication with the kernel and application threads. Based on its specific scheduling algorithm policy, scheduler achieves kernel system information, and application's scheduling information. This framework is suitable for user-level scheduler to obtain the distribution, diversity, and different scheduling information.Secondly, this paper implements two simple schedulers. One is an EDF-based scheduler, which completely replaces the kernel scheduler. The other is an assistant scheduler. It helps to improve the kernel's scheduling algorithm. The main process of the implementation is still completed in the kernel.Third, this paper improves a system call interface of the microkernel. This improvement helps to reduce the time when user-level scheduler goes into the kernel through this interface.