[LAU] kernel rt-patches future

Len Ovens len at ovenwerks.net
Tue Oct 21 21:05:23 UTC 2014

On Tue, 21 Oct 2014, Ulrich-Lorenz Schlüter wrote:

> Dear list,
> some of you may know this:
> http://lwn.net/Articles/572740/
> has there already been any thread about the future of the rt-patches?
> How to build a realtime audio system without rt-patches? Is rt-patches
> near dead, as there is no release since kernel 3.14? Guess this would
> have a very big impact on linux audio. Please tell if I'm missing something.

What it also says is that most of the RT bits for the Linux Kernel are 
already included in the mainline kernel. How much of what is left affects 

In my opinion, Much of the use for RT kernels in audio is to try and fix 
problems with system HW tuning. In my trials, I have found that using only 
a "lowlatency" kernel, I can get clean latency as low as my card is able 
to be set anyway (32 samples). The only xruns I get are from applications 
that do not shut down correctly or take to long starting up (that is they 
enable ports in jack before they are stable).

PC MB are not designed for low latency work, but rather large throughput 
and good graphics speed. Getting good low latency performance out of a PC 
requires tuning it, both SW and HW. Too many people see the RT kernel as 
some sort of magic bullet that will fix everything. The PC MB is designed 
for audio latency of 192 samples of 48k audio as minimum latency with the 
odd xrun being ok. (we are talking games and youtube here) Yes it does 
mean being picky about which MB is chosen, which CPU, which GPU, which GPU 
drivers (and it's settings), which slot the audio board is in, performance 
over ondemand, hyperthreading off, ... just to name a few.

The other thing the RT developers have pointed at is that changes to HW 
(multi-cores in particular) have opened up a whole new way of dealing with 
latency (for better or worse). A core or cores can be set aside for RT 
work only. With some processors other resources as well as just the 
processor core can be set aside from the OS such as memory.

But yes, the standard RT keneral development is seeing the money dry up.

Len Ovens

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