Re: [LAU] kernel rt-patches future

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
audio?

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
www.ovenwerks.net

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Received on Wed Oct 22 00:15:08 2014