Re: future of -rt kernels for realtime audio

[Robin Gareus <robin@gareus.org>]

On 07/06/2010 01:19 PM, Pedro Ribeiro wrote:
> Hi,
> 
> I've been using -rt kernels since 2.6.29 because I do realtime audio
> on my laptop.
> 
> The audio stability has been steadily improving since, and now I find
> that I can use 2.6.34 without the -rt patch and achieve the same
> stability as 2.6.33-rt - well, my latency requirements aren't that
> high, I just need to maintain 8.9ms completely stable, however before
> .34 it would be impossible without the -rt patch.

It's been possible to achieve low-latency for audio (using JACK) with
the vanilla kernel for a while now.
The -rt patch still has two major advantages:
 - it guarantees low latency.
   (pretty much a requirement for live-performance on stage)
 - it allows to assign scheduling priorities to IRQ handlers.
   (comes in handy for crappy machines that share the soundcard's IRQ)

As for your questions: I don't know the details, hopefully someone else
here can enlighten us. I'd be interested in that as well.

> So out of curiosity, what changed for .34? According to [1], on .33
> Raw Spinlock Annotation was introduced in the mainline kernel.
> However, as said above, I can't get the same performance than with
> .34.
> 
> I remember that I read somewhere that the one the biggest problems
> with latency requirements was the use of the BKL. Do you think there
> will be a significant improvement of latency (in specific cases of
> course) with the scheduled removal of BKL for 2.6.36?
> 
> Thanks for the help,
> Pedro
> 
> [1] http://www.osadl.org/Realtime-Linux.projects-realtime-linux.0.html

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Robin Gareus                           mail: robin@gareus.org
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