Finally nearing the finish line after 20+ years!

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Audiojunkie
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Finally nearing the finish line after 20+ years!

Post by Audiojunkie »

PREEMPT_RT Might Be Ready To Finally Land In Linux 5.20

https://www.phoronix.com/news/520-Maybe ... PREEMPT_RT

After years in the works, the "PREEMPT_RT" support for building a real-time Linux kernel might finally be mainlined for the upcoming Linux 5.20 cycle if the last few remaining bits are reviewed/signed-off on in time for next week's merge window.

The Linux real-time patch series has been getting smaller with time and quite close to crossing the finish line with just around 50 patches to be merged. This allows for building a real-time / fully preemptible kernel off the mainline code for embedded Linux systems.

For years there had been talk of PREEMPT_RT coming "soon" to mainline but ultimately didn't pan out. The Linux RT developers were held up by funding.

The change this year though was Intel acquiring Linutronix as the Linux consulting firm heavily involved in the PREEMPT_RT patches.

Now today the word is that PREEMPT_RT could be ready for Linux 5.20 if the last two blockers are sorted out this week. Sebastian Andrzej Siewior of Linutronix wrote on the kernel mailing list:
a polite ping for the series. This is one of two road blocks to get RT enabled in v5.20. I don't want to add any pressure just point out that I can't sit still for days since the end is near

Sebastian

That patch series are two signal/ptrace related patches needed for the PREEMPT_RT series. We'll see over the next two weeks during the Linux 5.20 merge window if the PREEMPT_RT patches are all aligned to finally be merged and there are no last minute issues or objections from Linus Torvalds or other key participants.
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Re: Finally nearing the finish line after 20+ years!

Post by tseaver »

@Audiojunkie
I don't want to add any pressure just point out that I can't sit still for days since the end is near.
Congratulations to you and the other devs who have wrestled with getting RT support into mainline!
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Re: Finally nearing the finish line after 20+ years!

Post by erlkönig »

A big thanks from my side, too.
Just for my understanding: that's "paralell" to the realtime-capabilities that we could use the last years with setcap. You merged the realtime-patch that was used (and will be used?) with set-rlimits?

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Re: Finally nearing the finish line after 20+ years!

Post by Audiojunkie »

I need to clarify something. 🙂 I just saw the news on Phoronix and posted it here. I’m not a developer. I’m not that smart. 😜
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Re: Finally nearing the finish line after 20+ years!

Post by Rodney »

hell yeah! can´t wait for it!
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Re: Finally nearing the finish line after 20+ years!

Post by sadko4u »

Still Virtualbox modules give kernel panic when working with RT kernel...
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Re: Finally nearing the finish line after 20+ years!

Post by GMaq »

sadko4u wrote: Thu Jul 28, 2022 9:10 am Still Virtualbox modules give kernel panic when working with RT kernel...
True, I had to move to VMWare... I would hope that if RT gets into the mainline Kernel Oracle will have no choice but to fix this..
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Post by novalix »

What about KVM/Qemu?
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Re: Finally nearing the finish line after 20+ years!

Post by Audiojunkie »

sadko4u wrote: Thu Jul 28, 2022 9:10 am Still Virtualbox modules give kernel panic when working with RT kernel...
I'm sure it wouldn't be easy, but I've run across solutions of how to work around this. IIRC, it has something to do with compiling the kernel modules--but at least there's a way if the generic kernel doesn't work. I imagine that developers will HAVE to make it work, since it's part of the generic kernel.
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Re: Finally nearing the finish line after 20+ years!

Post by sunrat »

Could be a similar hitch with Nvidia drivers. Nvidia currently include code to prevent building modules if RT is detected, although a workaround is possible. Nvidia driver issues are common on distro forums already for just stock kernels, I dread having to tell posters they have to set an environment variable before starting install.
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Re: Finally nearing the finish line after 20+ years!

Post by scott.thomason »

I don't understand why this is important anymore...aren't the real time scheduling features of a non-RT kernel good enough for everything? Seems to work fine for me...I use Liquorix and couldn't be happier.
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Re: Finally nearing the finish line after 20+ years!

Post by Audiojunkie »

scott.thomason wrote: Fri Jul 29, 2022 3:39 pm I don't understand why this is important anymore...aren't the real time scheduling features of a non-RT kernel good enough for everything? Seems to work fine for me...I use Liquorix and couldn't be happier.
Those "real time scheduling features of a non-RT kernel" that you are referring to, are exactly part of this project. Patch by patch, the real time scheduling features of the RT kernel have been mainlined into the generic kernel because of this project. The announcement is simply that the they are nearly complete with the work of getting "all" the real time patches mainlined. The news is important because it is a culminating achievement. The reason it is big news, is exactly why you are wondering why it isn't important anymore--because you've been continuously benefiting from this project. Now, the developers are finally almost done with mainlining everything in. That's cause for some congratulations to the developers for staying with it all these years to completely mainline ALL of the kernel patches. :)

EDIT: You use the Liquorix kernel which makes use of these patches (along with other things). Now, the generic kernel can do realtime too. It won't affect you at all, because the Liquorix kernel will do everything you need. But not all distros have the Liquorix or the Zen patches. Not all distros provide alternative kernels for those who want low latency. It is the users of Linux machines in these situations that will benefit from being able to get nearly the same functionality through a kernel boot parameter and through putting themselves into the realtime group. There are other things one can do to further tune your computer of course, but to the majority, and especially to those on distros that don't offer alterntive kernels and they don't want to compile code themselves, this project has use. And now, after nearly 20+ years, they are finally nearing the completion of the project started so long ago.
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Re: Finally nearing the finish line after 20+ years!

Post by scott.thomason »

Audiojunkie wrote: Fri Jul 29, 2022 8:15 pm Those "real time scheduling features of a non-RT kernel" that you are referring to, are exactly part of this project.
Ah, thanks for explaining that. I thought they were separate efforts.
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Re: Finally nearing the finish line after 20+ years!

Post by Audiojunkie »

I did some further reading regarding some of the questions that have come up regarding real time capability in the generic kernel. One thing that I forgot, that may have some bearing in this, is that NVIDIA open sourced their drivers. I don't use NVIDIA, so I had forgotten that. One of the biggest concerns that I remember reading in the past was that the biggest reason for the incompatibility between real time and NVIDIA was that the drivers were closed so that no one could work on compatibility. The door seems to be open for that problem to be resolved:

https://www.phoronix.com/review/nvidia-open-kernel

This is old news, of course, but I believe it is relevant to the conversation. I think the compatibilities will all be worked out and in the end there won't be compatibility problems with the real time aspects of the generic kernel. I can't guarantee this, but it certainly looks to me that this will be the end goal.
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Re: Finally nearing the finish line after 20+ years!

Post by Audiojunkie »

This article appears to further confirm my beliefs that the incompatibilities will be worked out in the end with the real time aspects of the generic kernel:

https://www.phoronix.com/news/Linux-6.0 ... sole-Print

The news isn't really anything special, but it does show that work is already being done to ensure compatibility and work around problems that can come from having real time capabilities merged with the generic kernel.
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