Linux has Real-Time now. What the fart does that actually mean?

20 years in the making. But what does a Real-Time Linux Kernel mean for most of us? Let's talk about how PREEMPT_RT works, what caused it to take over 20 years to get into mainline Linux, and what it means for the average Linux user.

[Zamsky]

Real-Time is huge for processing live audio where minimum possible latency is desirable.

[Amipotsophspond]

the final revisions to enable RT code after 30 years gold wrapped with a purple bow is the most bureaucratic thing I have seen in a long time, for some reason it reminds me of that futurerama quote "Don't quote regulation to me! I co-chaired the committee that reviewed the recommendation to revise the color of the book that regulation is in. We kept it gray."

[dr.benway]

I remember when you had to build your own RT kernels for audio Linuxes back in the day.

[Spacial_]

real time support will be a blessing for midi clocked applications

[DMBrownlee]

This and the recent FreeCAD 1.0 announcement bode well for CNC tinkerers using Linux.

[paherbst]

We'll be so screwed once Linus retires.

[timothywcrane]

Real time makes you not ingest data and digest data in chunks and choke. For Video processing and other places where "buffering" is disastrous (you thought it was bad watching ;) ) this is one helluva god thing for Linux. A person first looking into Linux for media like audio or video processing and design no longer has to be told to go straight into "how to recompile or change kernel" just in the very quick end to say "Windows and $500 bucks for this & That it has to be... ". This is a good thing.

[matthiasmartin]

I was just about to "ackshually..." when you said "20 years ago". So yes, very momentous - i remember those realtime special kernel builds from 20 years ago.

[innovationsanonymous]

Preempt ==> low latency

Rt kernel will be optimized for response time over throughput.

Want high throughput kernel for servers.

Want rt kernel for, e.g., audio, etc.

Want a normal kernel for desktops

[sillonbono]

Most of the benefits of the RT work are already applied in the regular kernel and this has been the case for a few years now. This is why Linux desktops running modern kernels are more responsive than ever. The battle for desktops is on improving the system scheduler to squeeze better user input responsiveness while remaining as fast as possible. 6.12 and beyond should see benefits regarding that.

[kevinpaulus]

I second the idea of having a scroll with the commits but also a ceremony for major merges.

[framegrace]

See a lot of misconceptions... RT doesnt make latency lower. It makes the time between an event and the code be predictible. That;s all.
If you have something sampling 100's of channels of adio or any measurement, all of them will have the same latency with the signal. Even if the latency is 30 seconds.
Thats what real time means.
In audio that means that if you are recording a guitar, a drummer, a bassist a singer and a whole orchestra, all of the mics will receive the audio in sync and be mixed in sync. The latency can be 1ms for a super duper multicore machine, or 10secons for a raspberry pi. It doesn't matter. If the buffers are big enough, the recording will be exactly the same.

[Lvvn]

I would argue that real-time might be a huge difference for linux gaming.
One of the most long-standing issues is audio skips and stutters which are happening even when overall system have plenty of resources to run the game.

[snap_oversteer]

Just a reminder that OS using Linux with PREEMPT_RT is still *not* true RTOS.

[paulreader]

Will be great for LinuxCNC which has required pre-empt RT for a long time but always suffered the need to carefully choose the distribution on which to install.

[TheLazyJAK]

The first thing i thought of when i heard the news was audio production similar to the asio in Windows. Im glad that hunch was somewhat correct!

[joemgj]

I have been using linuxcnc with real time kernels for my cnc router since 2011. One big hurdle to good performance is that the system management interface runs whenever it wants regardless of the operating system kernel leading to a lot of jitter in the timing of control loops. Apparently it is more important to check fan speeds than running my router. Solution is to disable acpi / smi.

[nickbarton]

Really helpful for a low cost, single CPU panel with a high priority controller application but a lower priority UI.

[MarkulonMarkerson-szxs]

Best update since kernel 3.11 for workgroups.

[gerhardbotha]

We have been using patches to make Linux pre-emptive and real time for ages. I see some stupid comments below. Just listen to what the nice man in the video is saying. Linux RT is great for industrial applications like drives or PLC’s using communications like ProfiNet etc where you set up things to execute in determined time slots and communicate etc at set intervals. So like he says, not necessarily fast, but necessarily predictable. You don’t need that in general computing. But things like signal processing etc can do with it. And no, it’s not for safety applications. But it can be part of a safety type application. RTOS etc are for much simpler applications where you don’t need a full on operating system like Linux. So you code according to the need. Either bare bones, or some scheduling scheme, or RTOS etc, or a full on OS.