Lmst

Linux 的 RT (Real-Time) 版本 PREEMPT_RT

在 Hacker News Daily 上看到的，Linux kernel 把 PREEMPT_RT 這個 RT patch 併入 official repository 了：「Real-time Linux is officially part of the kernel after decades of debate」。

這類需求可以在 RTOS 裡面看到完整的說明，大家常用的特性是確保反應時間這點，像是對汽車自動

https://blog.gslin.org/archives/2024/09/26/11993/linux-%e7%9a%84-rt-real-time-%e7%89%88%e6%9c%ac-preempt_rt/

#Computer #Linux #Murmuring #OS #Software #atomic #kernel #linux #output #patch #preempt_rt #printk #realtime #realtime

📊 #Linux kernel achieves real-time capabilities after 20 years of development

• 🔧 New #CONFIG_PREEMPT_RT option allows compiling a "Fully Preemptible Kernel (#RealTime)"

• 📝 Improvements to #Printk infrastructure ensure log messages don't interfere with time-critical tasks

• ⚙️ #RealTime support requires careful hardware and software optimization

• 🖥️ Unlikely to be relevant for most desktop, laptop, and server use cases

• 🤝 Inclusion in mainline kernel expected to attract new contributors for maintenance and development

• 🔍 Ongoing work to address remaining issues and optimize real-time support for specific components

https://www.heise.de/en/news/After-20-years-of-painstaking-work-Linux-kernel-now-real-time-capable-9935651.html

#DevOps

#PREEMPT_RT aka the #realtime support for #LinuxKernel hit #linux-next today! 🥳 👏

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?qt=grep&q=PREEMPT_RT

Still remains to be seen if those changes really makes it upstream during the 6.12 merge window and stick:

* It afaics is still unclear if some #printk prerequisites will be submitted for 6.12: https://lore.kernel.org/all/87ed5za2oj.fsf@jogness.linutronix.de/

* Troublemaking changes sometimes are reverted before the final, which in fact happened to some of printk prerequisites a while ago: https://lore.kernel.org/lkml/20220623145157.21938-6-pmladek@suse.com/

#kernel

v6 of the patch-set "add threaded printing + the rest" which "provides the remaining pieces of the #printk rework."[1] is now in #Linux-next – but as of now it's not yet clear if this will be merged for #kernel 6.12.

https://lore.kernel.org/all/ZthvGoJE26dOtsLm@pathway.suse.cz/

[1] e.g. the last big missing piece for #Realtime support through #PREEMPT_RT in the mainline #LinuxKernel. But note, this series does *not* provide an nbcon console driver. That will come in a follow-up series.

John posted v4 of the patch-set "threaded console printing as well as some other minor pieces" which "provides the remaining pieces of the #printk rework." -- e.g. the last big missing piece for #Realtime support through #PREEMPT_RT in the mainline #Linux #Kernel. But note, "this series does *not* provide an nbcon console driver. That will come in a follow-up series."

https://lore.kernel.org/all/20240827044333.88596-1-john.ogness@linutronix.de/

This comes hot on the heels of the "write_atomic() printing" entering -next: https://fosstodon.org/@kernellogger/113003819326920850

The improved #printk series "wire up write_atomic() printing" is now in -next again and thus slated for inclusion in #Linux 6.12. This is one of the last important bits for proper #REALTIME support with #PREEMPT_RT in mainline – but not the last, as this series does not include threaded printing or nbcon drivers, as those will come later: https://lore.kernel.org/all/ZsWxpVG8uZ9Nq26h@pathway.suse.cz/

A earlier version of the patch set was supposed to go into #kernel 6.11, but Linus was unhappy: https://lore.kernel.org/lkml/CAHk-=whU_woFnFN-3Jv2hNCmwLg_fkrT42AWwxm-=Ha5BmNX4w@mail.gmail.com/

John posted v3 of the patch-set with the "remaining pieces of the #printk rework" to support threaded console printing, which is last big missing piece missing to support #realtime with the mainline #Linux #kernel through #PREEMPT_RT:

https://lore.kernel.org/all/20240722171939.3349410-1-john.ogness@linutronix.de/

The last step in the #Linux #kernel #printk rework saga (the last big pre-requisite before #PREEMPT_RT can be mainlined) is getting closer:

John submitted the printk patch series "add threaded printing + the rest", which '"provides the remaining pieces of the printk rework. All other components are either already mainline or are currently in linux-next. […] Note that this series does *not* provide an nbcon console driver. That will come in a follow-up series."'

https://lore.kernel.org/all/20240603232453.33992-1-john.ogness@linutronix.de/

Another step closer for #PREEMPT_RT support in the upstream #LinuxKernel:

The #printk patch series "wire up write_atomic() printing"[1] is now in #linux-next[2] and thus slated for inclusion in #kernel 6.11. 🥳

Note, that series does _not_ include threaded printing or nbcon
drivers. Those features will be added in separate follow-up
series.

[1] https://lore.kernel.org/all/20240527063749.391035-1-john.ogness@linutronix.de/

[2] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?qt=grep&q=Ogness

Another small step to get #RT aka #Realtime aka #PREEMPT_RT support mainlined was taken, as more preparations for introducing #printk kthreads were merged for #Linux #kernel 6.7: https://git.kernel.org/torvalds/c/2a80532c0745e140852e6b579bbe8371332bb45d

That work comes from this series:
https://lore.kernel.org/all/20230916192007.608398-1-john.ogness@linutronix.de/#t

But some more work is needed to finally make the #LinuxKernel printk stack be rt capable, as threaded printing, atomic printing regions, or nbcon drivers are still missing afaics.