The PREEMPT_RT Locking Code Is Merged For Linux 5.15

[tomas]

If someone is interested what all of this "real time" stuff is actually about, here is an LWN article from October last year:

https://lwn.net/Articles/837019/

One key quote:

"He noted that a lot of people mistakenly think that all tasks in a realtime system are realtime, while most of them are not."

[sinepgib]

Nice to see it is in Debian. I hope it is also in other distributions, or that it will come to other distributions.
Unfortunately it is not in Ubuntu, but hopefully that changes soon.

It seems for Arch you need to install from AUR (or build it yourself, but that's impractical): https://wiki.archlinux.org/title/Realtime_kernel

EDIT: I mean, it's technically building it yourself too, but you don't need to manually create a config, which is the actually impractical part, the build will just happen without interaction.

[uid313]

Not sure what Ubuntu is doing but it is in Debian
https://packages.debian.org/bullseye...image-rt-amd64
https://packages.debian.org/bullseye...0.0-8-rt-amd64

Nice to see it is in Debian. I hope it is also in other distributions, or that it will come to other distributions.
Unfortunately it is not in Ubuntu, but hopefully that changes soon.

[sinepgib]

BTW, this is the very same kernel configuration that Google uses across Android + ChromeOS + Stadia.
If hard-RT really would've been a "magic bullet", then why isn't it used everywhere?

Most likely not the case (the likely reason is degraded performance for no practical gain for their use case), _but_ since it affects some quite core components and upstream wouldn't debug something added by downstream, it would mean extra resources from whoever ships it, so a big no for "using everywhere" is being out of tree.
As someone else mentioned, even soft real time config triggers bugs in some drivers that aren't triggered by the generic one.

[mppix]

Ubuntu offers a generic kernel (default) and a low latency kernel (in the repository).
I don't know if other distributions does too.
I hope that Ubuntu (and other distributions) will now start to also offer a RT kernel.

Not sure what Ubuntu is doing but it is in Debian
https://packages.debian.org/bullseye...image-rt-amd64

https://packages.debian.org/bullseye/linux-image-5.10.0-8-rt-amd64

[mppix]

Funny that you imply I was missing the point when all along I was arguing on why a hard-RT Linux kernel is exactly _not_ for the average PC user!

You gave us a lecture why folks should not care about this. However, folks are not just desktop users around here.

And when I said that said average desktop user is best served with a 1000 Hz + full kernel-level preemption kernel (PREEMPT) [please don't force me to prove you wrong on this either!], you again disagreed with me, even though I already had written what you were trying to lecture me on.

No, this is incorrect. Low latency may be good for gaming (mainly for inputs) but consumes more power. Your mom prefers a laptop with battery over fps.

PS. I was a lot less "lecturing" than whatever your posts intend to be.

[uid313]

Ubuntu offers a generic kernel (default) and a low latency kernel (in the repository).
I don't know if other distributions does too.
I hope that Ubuntu (and other distributions) will now start to also offer a RT kernel.

[jabl]

If the so-called »lowlatency« kernel offers the best of both worlds, then why isn't the lowlatency kernel the default kernel? Why is there a "generic" kernel? Why does the lowlatency kernel configuration option even exist? Does the lowlatency kernel have drawbacks over the "generic" kernel?

Last I checked, there is a small throughput hit when using the lowlatency kernel. Not nearly as big as with the full RT kernel, but still.

Also, at least several years ago there were many drivers that caused crashes when compiled in lowlatency mode due to incorrect locking. So distributions didn't want to offer it as the default, hence it doesn't get as much testing, hence those problems don't get fixed. Chicken and egg.

[uid313]

I like how almost everyone [You're explicitly excluded perpetually high] in this thread likes to respond in theoretical terms (which usually means talking out of their collective a$$es) without contributing any helpful advice or hint in the end anyway; most likely because they never have used a hard-RT Linux kernel in the first place!

So let me change that for you:

AFAIK, you are running Ubuntu LTS or a derivative distro based on it, right?
Great, this is the very foundation for the absolute best Linux user experience and I applaud you for this correct decision!

Now, all you have to do is to install the so-called »lowlatency« kernel officially supported by Canonical and get rid of the "generic" one.
This will net you a 1000 Hz + fully-preemptible soft-RT LInux kernel, which basically means that you get most of the benefits of a hard-RT kernel minus the drawbacks like severely degraded performance.
[For anyone doubting the degraded performance part: Just compare with advanced software like RPCS3 & and watch your FPS plummet hard with a hard-RT kernel.]

BTW, this is the very same kernel configuration that Google uses across Android + ChromeOS + Stadia.
If hard-RT really would've been a "magic bullet", then why isn't it used everywhere?
Wouldn't Google want their Android OS to perform better than Apple's iOS?
And how come Valve isn't going to ship their upcoming Steam Deck with a hard-RT kernel?
Are all of these corporations & their employees really that dumb?

Point is, hard-RT Linux has its places & use-cases, and I'm glad that it's getting upstreamed so that more companies & individuals can pick up on it more easily where safety is the top-priority.
However, for the average desktop Linux user, I fear this will give them a false sense of having a superior kernel at their disposal, when in fact the opposite will be true.

Therefore, with a 1000 Hz + PREEMPT kernel, you already do get the best of both worlds!

Yes, I am running Ubuntu.

If the so-called »lowlatency« kernel offers the best of both worlds, then why isn't the lowlatency kernel the default kernel? Why is there a "generic" kernel? Why does the lowlatency kernel configuration option even exist? Does the lowlatency kernel have drawbacks over the "generic" kernel?

[Linuxxx]

You _are_ still missing the point - this is not for your PC, at least not for fps.
Re question: I run it as control platform on embedded systems.
If I have some time, I may try out doing real-time sampling/processing of audio/video that could have applications in tone studios or stage installations.
Maybe, I'll tie it to hard real-time ethernet. Do you have an issue with that as well?
(hint: that is not for gaming either but it can used to connect professional AV equipment..)

Funny that you imply I was missing the point when all along I was arguing on why a hard-RT Linux kernel is exactly _not_ for the average PC user!
And when I said that said average desktop user is best served with a 1000 Hz + full kernel-level preemption kernel (PREEMPT) [please don't force me to prove you wrong on this either!], you again disagreed with me, even though I already had written what you were trying to lecture me on.

Therefore, let's leave it at that, or else I will need to dig out a quote from Ingo Molnar...