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Re: Audio SIG - Jacklab spin



On Thu, 2008-07-10 at 17:40 +0200, Harald Hoyer wrote:
> Michal Schmidt wrote:
> > On Thu, 10 Jul 2008 13:40:26 +0200
> > Harald Hoyer <harald redhat com> wrote:
> > 
> >> Anyone interested in an audio SIG?
> >>
> >> We could create a jacklab like spin ( http://jacklab.org/ ) with
> >> jackd as the main audio daemon.

(or Ubuntu Studio, the Gentoo pro audio overlay, 64Studio, etc, etc,
pretty much all big distros already have it)

> > Would the absence of a real-time kernel variant in Fedora be a problem
> > for such a spin? 

Yes.

> > Fedora kernel only has voluntary preemption enabled.
> > All the audio-specialized distributions I've heard about ship with an
> > RT-patched kernel.
> > 
> 
> Absence is no "problem" on a modern desktop (my desktop :-) ), though a 
> real-time kernel would definitely improve the latency for slower systems.

Nope. It is a problem. 

A stock Fedora kernel can have latency problems if you use jackd with 64
or 128 frames per period[*]. One hiccup is enough to ruin a performance
or a recording session. That is why other audio oriented distros use a
realtime patched kernel (as does Planet CCRMA, which I maintain). 

You could define your "target user base" to not need that level of
performance, and then sidestep the issue. But then you can't compare a
hypothetical Fedora JackStudio or whatever distro with other audio
oriented distros that have a realtime patched kernel. 

> Maybe we could "maintain" a kernel-rt package or persuade our RHEL5 kernel team 
> to provide a rt-kernel (with the benefit of more QA :) ).

I've been "maintaining" one for Planet CCRMA since 2001. It is not fun
(well, it used to be, many years ago) and it is a worthy task for
Sisyphus. I made some noise in the fedora audio list a while back about
this, but there's no manpower for doing a realtime kernel on Fedora.
RedHat itself does have a realtime patched MRG kernel for RHEL. 

-- Fernando

[*] depends on your particular hardware configuration, sound card model,
interrupt sharing, usage patterns, and the phase of the moon for all I
know :-)



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