Design And Implementation Of Linux2.6 Kernel New High-precision Timer

With the dramatic increase in consumer electronic market, real-time services as reperesented by video and audio processing, are drawing growing public attention. As an traditional time-sharing operating system, the design goal of Linux is focusing on maximum throughput, thus its real-time capability has been less than satisfactory. Benno Senoner developed a suite of benchmark tools and found that the worst case might hit even 100 millisecond delay, taking version 2.2 and 2.4 Linux kernel as testing target. This result will obviously be unable to meet the multimedia processing needs. One crucial aspect to enhance the real-time capability of Linux is to improve the accuracy of kernel timer. Since Real-time system is strictly controlled by time sequence, the accuracy of timers will affect the granularity of timing. Linux traditionally relies on interval timer interrupt to implement fair share of CPU time in turn between processes. On various platforms the interrupt frequency of interval timers is set to between 100HZ and 1000HZ, therefore the timing accuracy has been restricted to between 1ms and 10ms. This granularity is rather coarse for real-time applications.In order to improve the real-time capability of Linux, the Kansas University made a poineering project named KURT-Linux, in which whe UTIME component implemented one kind of high resolution timer. Later, MontaVista company made a similar effort in their HRT project, which was primary used for Carrier Grade Linux.This paper describes the design and implementation of a new approach to achieve high-resolution timer based on Linux 2.6. This approach implements the hight-resolution timer facilities independently, thus can get rid of the unacceptable worst-case response time in UTIME and HRT. Furthermore, in order to ensure portability, some abstract level related to the kernel clock system were introduced. After a series of tests and improvement, the experimental results show this approach fully satisfy the real-time needs, and it also provides a solid foundation for the achievement of certain advanced features such as dynamic ticks.