[LAU] rt-patch 23-Jul-2011

Robin Gareus robin at gareus.org
Sun Jul 24 16:59:10 UTC 2011

Hi Ralf,

On Jul 24, 2011, at 4:12 AM, Ralf Mardorf wrote:

> 3.0-rt2
> So, the "rt patch emulation" ex kernel 2.6.39 might be less good than a
> kernel that is patched?

It's not "emulation". A big part of the RT patch (e.g. threaded IRQ handlers) was been merged into 2.6.39.
The goal of the Preempt-RT patch is to eventually end up completely in the vanilla (aka mainline) kernel.

http://lwn.net/Articles/440064/ is a nice read on the current state of it.

> Until now I build
> linux-image-
> linux-image-
> but I only produced music with until now, dunno if 2.6.39
> isn't as good as a kernel-rt.
> Any information, experiences?

I've been running 2.6.39 ever since it came out and used it for production. I can't tell a difference between it and the rt-patched 2.6.33 for general audio/video production. Neither will produce x-runs - unless I do sth stupid or overload the system.

Threaded IRQ handling of the audio-interface and [high priority] FIFO scheduling are the important parts for low-latency audio and they're mainline in 2.6.39 (FIFO scheduling was for a long time already).

There's a lot of small (but complex) things the RT patch does that are not in mainline yet (e.g pre-emptible memory-management, sleeping spinlocks) and can improve the guaranteed response-time of dedicated [audio] processes. However the gain [of code available in RT vs what is already mainline] is rather small when compared to latency requirements of audio (us vs. ms) and thus can be neglected on most systems. It'll probably give you an edge though.

Long story short: If you just want to make music: stick with 2.6.39 or 3.0 - If you have the time and ability to debug: give 3.0-rt3 a go. 

Even though the impact of the RT-preemt patch on pro-audio is becoming less dramatic. It's a great project and important project.


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