REDESIGNING THE BSD TIMER FACILITIES

We describe a reimplementation of the BSD timer facilities. Older BSD kernels take time proportional to the number of outstanding timers to set or cancel timers. Our implementation tin NetBSD) takes constant ti me to start, stop, and maintain timers; this leads to a highly scalabl e design that can support thousands of outstanding timers without much overhead. Unlike the existing implementation, our routines are guaran teed to lock out interrupts only for a small, bounded amount of time, We also extend the setitimer() interface to allow a process to have mu ltiple outstanding timers, thereby reducing the need for users to main tain their own timer packages. The changes to the kernel are small (54 8 lines of code added, 80 removed) and are available on the World Wide Web. (C) 1998 John Wiley & Sons, Ltd.