Real-Time Patches Updated Against The Linux 6.8 Kernel

[ayumu]

You're clueless, but it's nothing new.

What's with your attitude. Get help.

Show me tested kernel config and show Windows results as well.

I already told you how to verify. I'll simply restate if it helps:

You can run cyclictest on your desktop or workstation yourself, with SCHED_FIFO policy. Leave it running in the background for a while (I recommend a week, but it is likely it will be immediately bad), and you'll see how bad Linux does.

I have verified it across a range of hardware, so you won't miss it. The only relevant column is the MAX one. The unit is microseconds. 2ms(2000) is more than enough to break pro audio, but you will eventually see it go above 20ms (20000). That is terrible.

Using the RT patchset fixes this problem, and peak stays reasonable.

That's because Linux users have been conditioned to have lower expectations.

Very true.

No desktop OS needs hard RT. This is primarily needed for device control. So MAYBE professional audio.

You seem confused. Linux, even with the RT patchset, does not offer hard RT. It is only soft RT.

Soft RT is just about offering the mechanisms (such as realtime scheduling policies), and trying really hard to keep the latency low for realtime tasks. Linux offers Soft RT by default (posix realtime scheduling), but it isn't very good at keeping the latency down.

Hard RT is about formal verification that the deadline will never be missed. This cannot be done on Linux, due to its TCB size (covering the whole kernel, tens of millions of LoCs).

Few RTOSs actually have this formal verification. The best of which is seL4, which offers isolation (unlike the other verified ones) and formal proofs that extend far beyond any OS.

Soft RT is considered good enough for audio work, whereas Hard RT is for critical applications where people could die or millions could be lost if a deadline is not met. Linux is not suitable for those, nor are Windows or MacOS.

Dude. Windows has never been RT. Linux has always done better in this arena.

Windows offers Soft RT ever since Windows 95: https://beej.us/guide/win95sch.html

It behaves better (and so does NT) than Linux does without its RT patchset. For instance, Windows can handle realtime pro audio pipelines as-is, whereas Linux absolutely needs the realtime patchset.

You can easily verify this with the free tool DPC Latency Checker. The principle of operation is the same as cyclictest. It measures time from (scheduled, via timer) interrupt and when the ISR actually runs.

Windows is very good at never going above 500us, unless you have a bad driver, which is why the tool exists.

With the RT patches Linux is, however, even better than Windows at this, typically managing to keep max scheduling latency under 100us. Almost as good as AmigaOS was in the original Amiga computer.

[sophisticles]

But Intel can't do RT anyway because of SMI. Wish intel would fix that AND preempt-rt already.

Where did you get the idea that intel can't do real time?

https://ubuntu.com/blog/real-time-kernel-technical

Before people get excited about real time patches, I suggest you try a distro with a RT kernel already configured, like Ubuntu Studio.

I have tried it a couple of times and I hated it every single time.

I also tried a real time kernel with Manjaro and it sucked.

The latest release of MX Linux features a RT kernel, only tried it on a VM, seemed pretty good.

[sophisticles]

Dude. Windows has never been RT. Linux has always done better in this arena.

I love going fishing:

https://learn.microsoft.com/en-us/windows/iot/iot-enterprise/soft-real-time/soft-real-time

I have been saying for decades that in order to be a Linux advocate you need to meet the following two criteria:

1) You need to believe that you know what you are talking about.

2) The opposite needs to be actually true.

When both these conditions are met, then you have a Linux advocate.

[poncho524]

Where did you get the idea that intel can't do real time?

System Management Mode screws it up.

[ayumu]

20ms audio latency is unnoticeable for anything other than music production tasks. You certainly won't notice it on calls or media or even games.

Just in case I have to ask: Do you realize 20ms is more than one frame at 60Hz?

Do you also realize human hearing has lower latency than human sight?