20 years later, real-time Linux makes it to the kernel

Wow finally, it seems like yesterday when first encountered the real-time Linux kernel proposal.<p>It&#x27;s a long time overdue and congrats to the real-time Linux time for the tenacity. The fact that it&#x27;s included after eBPF being accepted to the Linux kernel but better late than never. Now we can preempt eBPF codes to make it even faster and responsive.<p>It will be very interesting to run real-time Linux on Raspberry Pi interfacing with Pi Pico for IoT monitoring, sensing and actuating communicating over bidirectional BiSS interface [1].<p>[1] BiSS: High speed open-source digital interface for IoT sensors and actuators:<p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=41516826">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=41516826</a>

Wow that sounds like a hell of an achievement. Here is the commit to the print_k function they mentioned as the final hurdle [1]. I have no idea what it does but maybe someone else here does. I wonder if the RT stuff will remain behind a config flag or become the default eventually. Is there any reason to not just have RT on by default?<p>I remember I had some nasty sound distortion issues on a Windows VFIO VM and it came down to events&#x2F;interrupts not being handled quickly enough. I wonder what happens with an RT kernel and the VM thread having high priority in that situation.<p>[1] <a href="https:&#x2F;&#x2F;git.kernel.org&#x2F;pub&#x2F;scm&#x2F;linux&#x2F;kernel&#x2F;git&#x2F;torvalds&#x2F;linux.git&#x2F;commit&#x2F;?id=c903327d3295b135eb8c81ebe0b68c1837718eb8" rel="nofollow">https:&#x2F;&#x2F;git.kernel.org&#x2F;pub&#x2F;scm&#x2F;linux&#x2F;kernel&#x2F;git&#x2F;torvalds&#x2F;lin...</a>

Anyone know if this will have any impact on low-latency linux audio? The article calls out JACK, but I&#x27;d guess the new standard for musicians recording on Linux is pipewire. So if pipewire either found some workaround or has been enabling a real-time module, I suppose those end users wouldn&#x27;t see a difference.

If anyone wants to try multiple kernels on their machine, here&#x27;s how you&#x27;d do it with systemd-boot<p><pre><code> ## install mainline, bleeding, secure, stable, and stable realtime, mainline realtime pacman -S linux linux-zen linux-hardened linux-lts linux-rt-lts, linux-rt ## and I guess, soon to be: linux-rt </code></pre> And then add the following 5 bootloader entries as separate files<p><pre><code> #&#x2F;boot&#x2F;loader&#x2F;entries&#x2F;linux{,-zen,-hardened,-lts,-rt-lts,-rt}.conf title Linux {Main,Zen,Hard,LTS,RT-LTS,RT} linux &#x2F;vmlinuz-linux{,-zen,-hardened,-lts,-rt-lts,-rt} initrd &#x2F;initramfs-linux{,-zen,-hardened,-lts,-rt-lts,-rt}.img options root=PARTUUID=&quot;the-part-uuid-of-your-root-partition&quot; rw </code></pre> and after those 5 files are in place, do a `bootctl update`

Nice. Real-time Linux used to be a joke, but apparently now it works.<p>The sheer complexity of making much of kernel space preemptable is scary. There&#x27;s too much running in kernel space.

Lots of testing (and funding, I think) by OSADL, who nobody seems to know: <a href="https:&#x2F;&#x2F;www.osadl.org&#x2F;OSADL-QA-Farm-Real-time.linux-real-time.0.html" rel="nofollow">https:&#x2F;&#x2F;www.osadl.org&#x2F;OSADL-QA-Farm-Real-time.linux-real-tim...</a>

&gt; the Linux kernel is fully preemptible,<p>So this means there are no critical sections or interrupts being disabled anywhere in kernel code when PREEMPT_RT is enabled?

A buddy of mine used Trinux RTK and Wind River RTLinux in a commercial audio console product back in the 00&#x27;s. There were several efforts back then.

I don’t know much about RTOS. But am aware that JPL uses VxWorks for planetary rovers and orbiters. So wondering if JPL or other entities will replace VxWorks with a Linux RTOS implementation at some point.

&gt; Unlike general-purpose operating systems like Windows or macOS.<p>FYI, there appears to be minor one, too: it&#x27;s called Linux.

I wonder if this will improve emulation compatibility?