Abstract: Precise timing is very important for the correct scheduling and timely response of task As a time sharing system, Linux’s 10?ms timing resolution is necessary and appropriate Many real time applications demand microsecond resolution timers, so Linux timer is too coarse for real time systems But simply increasing the timing resolution would lead to excessive and unsupportable overhead In order to improve Linux’s real time performance, a fine grain timer scheme implemented in RFRTOS based on Linux is discussed Experiments show that the improvement provides a fine grain timer with less cost