Improving the Real-time Performance of a General-purpose OS through Timer Shielding

With the increase in hardware performance of modern embedded systems, general-purpose operating systems (OS) such as Linux are commonly used as embedded OSs. Furthermore, the use of multi-core CPUs enables Linux to improve its real-time performance even on high-load scenarios which is rather hard to achieve on single-core CPUs thanks to its “CPU affinity” functionality. However, we found two issues in the current version of the Linux kernel: the CPU affinity of some kernel threads cannot be specified; and the use of timer cascading (use of multiple hardware timers to count time) increases the worst-case response time of real-time tasks. In this paper, we classify the cores in a multi-core CPU into 2 different groups: cores which require real-time performance guarantees; and cores which do not require such guarantees. Then, we propose and evaluate a method that improves the real-time performance of the system by disabling timer cascading on cores which require real-time performance guarantees.