Performance Evaluation of GNU/Linux for Real-Time Applications

Abstract: GNU/Linux systems have become strong competitors in the embedded real-time systems segment. Many companies are beginning to see the advantages with using free software. As a result, the demand to provide systems based on the Linux kernel has soared. The problem is that there are many ways of achieving real-time performance in GNU/Linux. This report evaluates some of the currently available alternatives. Using Xenomai, the PREEMPT_RT patch and the mainline Linux kernel, different approaches to real-time GNU/Linux are compared by measuring their interrupt and scheduling latency. The measurements are performed with the self-developed Tennis Test Tool on an Intel XScale based Computer-On-Module with 128MB of RAM, running at 520MHz. The test results show that Xenomai maintains short response times of 58ms and 76ms with regard to interrupt and scheduling latencies respectively, even during heavy load of the Linux domain. When the Xenomai domain is loaded as well, responsiveness drops to 247ms for interrupt latency and 271ms for scheduling latency, making it a dead race between Xenomai and the PREEMPT_RT patched kernel. The mainline kernel performs very well when not subjected to any workload. In the tests with more load applied, performance deteriorates fast with resulting latencies of over 12ms.