Hrtimers and Beyond: Transforming the Linux Time Subsystems

Several projects have tried to rework Linux time and timers code to add functions such as high-precision timers and dynamic ticks. Previous efforts have not been generally accepted, in part, because they considered only a subset of the related problems requiring an integrated solution. These efforts also suffered significant architecture dependence creating complexity and maintenance costs. This paper presents a design which we believe provides a generally acceptable solution to the complete set of problems with minimum architecture dependence.

The three major components of the design are hrtimers, John Stulz's new timeofday approach, and a new component called clock events. Clock events manages and distributes clock events and coordinates the use of clock event handling functions. The hrtimers subsystem has been merged into Linux 2.6.16. Although the name implies "high resolution" there is no change to the tick based timer resolution at this stage. John Stultz's timeofday rework addresses jiffy and architecture independent time keeping and has been identified as a fundamental preliminary for high resolution timers and tickless/dynamic tick solutions. This paper provides details on the hrtimers implementation and describes how the clock events component will complement and complete the hrtimers and timeofday components to create a solid foundation for architecture independent support of high-resolution timers and dynamic ticks.