Impact of the Linux Real-time Enhancements on the System Performances for Multi-core Intel Architectures

Abstract

Embedded Linux became a dominant choice in the embedded entertainment and mobile systems. Their adoption in widely used control applications is the second phase of their embedded market domination. One of the most important criteria of the control RTOS is their determinism/overhead ratio. Actually, many extensions exist to bring real-time capability into the Linux kernel. On the other hand standard computer architecture become widely adopted in the embedded market, with a large variety of performances and power requirement.In this paper, we study the impact of timing enhancement offered by various real-time Linux kernel extensions and their impact into the overall system performance. The obtained results are compared with the standard and server kernels performances.We used for our study a multi-core Intel® based architecture since we considered the trend of the embedded control market for this kind of architectures.In our work we studied two metrics to reflect the performance of the studied kernel that are latency and throughput. Such work can be used to orient the adoption of real-time Linux extension for a given hardware architecture to reach control application requirements.

Impact of Machine Virtualization on Timing Precision for Performance-critical Tasks

“…In the context of multiprogrammed computing system, it's possible to distinguish several main types of tasks [11,12]. According to this classification, we distinguish the following load scenarios and create corresponding testbeds for the experiment:…”

Real-time capabilities in the standard Linux Kernel: How to enable and use them?

“…Also, this patch presents new operating system enrichments to reduce both maximum and average response time of the Linux kernel [8]. These enhancements were progressively added to the Linux kernel to offer real-time capabilities.…”

“…The most important enhancements are: High resolution timers ( a patch set, which is independently maintained by Thomas Gliexner [15], which allows precise timed scheduling and removes the dependency of timers on the periodic scheduler tick [16]) , complete kernel preemption, interrupts management as threads, hard and soft IRQ as threads, and Figure 1: Standard 2.6 Linux kernel with preemption priority inheritance mechanism. Some of these new features like threaded IRQ are currently pushed to the mainline kernel by the patch maintainers [8].…”

“…It allows almost the whole kernel to be preempted, except for a few very small regions of code ("raw_spinlock critical regions"). This is done by replacing most kernel spinlocks with mutexes that support priority inheritance and are preemptive, as well as moving all interrupts to kernel threads [8,14].…”

“…The most adopted solutions are RTLinux/RTCore, RTAI, Xenomai and the PREEMPT-RT [7] patch. Each one of these real-time enhanced kernels has its internal architecture, its strength and weaknesses [8]. All these approaches operate around the periphery of the kernel, except PREEMPT-RT patch which is mainlined in the current kernel and used by great actors such as WindRiver in their Linux4 [9] solution.…”