Clarifying the Linux Real Time Issue

我最近发布了一个article about the increasing development and availability of Linux-powered automation devices. This is a clear industry trend that’s unavoidable for anyone following the automation technology industry.

发布文章后不久，我听到了一位写道的读者：“我读了你的文章，我很惊讶你会宣传任何人都会使用Linux的想法。它甚至不是一个实时控制系统。它可用于非关键应用，但文章意味着行业正在采用它的一切。“

This reader brings up a valid point. Linux is not a real-time operating system (OS) in and of itself. As Vibhoosh Gupta of GE Automation & Controls noted in the original article, GE uses “Type 1 hypervisor technology to run a real-time OS, such as VxWorks, running traditional control loops alongside our PAC Edge technology operating on Linux.”

在收到读者电子邮件后，他进一步解释说，由于Linux不是实时操作系统，因此应该为需要确定性的关键应用程序来谨慎使用。

“That is the primary reason GE Automation & Controls uses the Type 1 hypervisor to run both VxWorks and Linux simultaneously, safely and cooperatively on the controller,” he said. “The idea is to run critical applications like the control loop on VxWorks and then run non-deterministic analytics on Linux. The analytics algorithms then advise the control loop running on VxWorks in real-time to optimize the process for better outcomes.”

Adding to Gupta’s point, Charlie Norz noted that Wago’s Linux-based controllers “use Linux with a real-time preempt that is commonly used in time-sensitive applications.”

Opto 22 also uses Linux real-time extensions in its Linux devices, said Benson Hougland. These real-time extensions for Linux are why it is being used in “more and more mission critical systems all over the world,” he said.

引用这一点实时LinuxandLinux FoundationWiki sites, Hougland highlighted the continuing work that is being done on the PREEMPT_RT real-time Linux extension.

Linux基金会于2015年10月推出了实时Linux（RTL）协作项目。根据该项目，该项目是“由行业专家创立，推进机器人，电信，制造业和医疗行业的技术。RTL协作项目的目的是将Premempt_RT补丁的主要连接。“

While there are plenty of mission critical applications running Linux OS with real-time extensions—as highlighted by GE, Opto 22 and Wago—the Linux Foundation notes on its site that there remains “much work to be done.”

这项需要更多关于开发自动化技术的工作是一个正在进行的，由于业界在两十年前在现代化的计算技术开发新产品以来，不断缺乏争议。第一个关注领域之一是在20世纪90年代后期引入厂房以太网。

“Remember,” said Hougland, “the entire industry once declared Ethernet would never make it to the plant floor!”

But now, Ethernet is close to becoming to the standard plant floor networking technology of preference—even though work remains to be done to optimize its use there with the development oftime-sensitive networking.

这种持续automa的开发工作tion technologies has only become more widespread with the rise of the smart manufacturing and Internet of Things trends currently transforming industry—all of which serves to make the Linux real-time issue just another example of how an array of technologies are being adapted to industrial applications to address specific needs.

With that said, anyone interested in using Linux for control applications should heed the reader’s caution about it not being a real-time OS. Recognize its current potential, but also remain aware of its limitations.

A quote by Linux inventor Linus Torvalds on the Real-Time Linux site may express it best: "Controlling a laser with Linux is crazy, but everyone in this room is crazy in his own way. So if you want to use Linux to control an industrial welding laser, I have no problem with your using PREEMPT_RT."