2 weeks Ago By Kevin Purdy
Enlarge / Cutting metal with lasers is hard, but even harder when you don't know the worst-case timings of your code. Getty Images reader comments 31 As is so often the case, a notable change in an upcoming Linux kernel is both historic and no big deal. If you wanted to use "Real-Time Linux" for your audio gear, your industrial welding laser, or your Mars rover, you have had that option for a long time (presuming you didn't want to use QNX or other alternatives).
Universities started making their own real-time kernels in the late 1990s. A patch set, PREEMPT_RT , has existed since at least 2005. And some aspects of the real-time work, like NO_HZ , were long ago moved into the mainline kernel, enabling its use in data centers, cloud computing, or anything with a lot of CPUs.
But officialness still matters, and in the 6.12 kernel, PREEMPT_RT will likely be merged into the mainline . As noted by Steven Vaughan-Nichols at ZDNet , the final sign-off by Linus Torvalds occurred while he was attending Open Source Summit Europe.
Torvalds wrote the original code for printk , a debugging tool that can pinpoint exact moments where a process crashes, but also introduces latency that runs counter to real-time computing. The Phoronix blog has tracked the progress of PREEMPT_RT into the kernel, along with the printk changes that allowed for threaded/atomic console support crucial to real-time mainlining. What does this mean for desktop Linux? Not much.
Beyond high-end audio production or replication (and even that is debatable ), a real-time kernel won't likely make windows snappier or programs zippier. But the guaranteed execution and worst-case latency timings a real-time Linux provides are quite useful to, say, the systems that monitor car brakes, guide CNC machines, and regulate fiendishly complex multi-CPU systems. Having PREEMPT-RT in the mainline kernel makes it easier to maintain a real-time system, rather than tend to out-of-tree patches.
It will likely change things for what had been, until now, specialty providers of real-time OS solutions for mission-critical systems. Ubuntu, for example, started offering a real-time version of its distribution in 2023 but required an Ubuntu Pro subscription for access. Ubuntu pitched its release at robotics, automation, embedded Linux, and other real-time needs, with the fixes, patches, module integration, and testing provided by Ubuntu.
"Controlling a laster with Linux is crazy," Torvalds said at the Kernel Summit of 2006 , "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." Roughly 18 years later, Torvalds and the kernel team, including longtime maintainer and champion-of-real-time Steven Rostedt , have made it even easier to do that kind of thing.
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