Preliminary Research On Time Subsystem In Exokernel

The abstraction layer in traditional operating system limits flexibility and performance of top-level applications and exokernel improve the limits above by getting closer to hardware. This thesis explores time subsystem in exokernel and nano-kernel. Then thesis implements time subsystem in JOS which is similar to exokernel operating system and put the implementation of High Precision Event Timer in JOS into embedded hypervisor XtratuM to improve precision of time interrupt.The implementation of JOS time subsystem follows the rules that exokernel should separate policy and mechanism: control of hardware in kernel space and abstraction in user space. All functions above are provides by user library. Abstraction of time subsystem contains clock source, clock event and timer. The abstraction is a policy which top-level application can use to control how system mange the time. The access to hardware includes map and control different clock.Though High Precision Event Timer is implemented in XtratuM, old clock Programmable Interval Timer is also reserved to schedule task due to different situation. The implementation in XtratuM mainly includes driver of High Precision Event Timer and top-level time interrupt in Linux. The implementation of driver is ported from time subsystem in JOS. Before designing top-level Linux time interrupt, whole process of Linux time interrupt should be analyzed.The evaluations of time interrupt show that the real time consumed by time interrupts is different from theoretical and this difference is constant. This mainly due to the context switch in interrupt and time spent by time interrupt handler. The precision improved by High Precision Event Timer is less than it should be due to the situation that when time interrupt period is small, real time consumed by time interrupts changes little though time interrupt period changes. The reason it changes little is also due to time of context switch and handler.