[LAU] A surprisingly stupid RT priority question

Paul Davis paul at linuxaudiosystems.com
Mon Dec 3 01:01:51 UTC 2012

nice has absolutely nothing to do with this, and if it has any effect, it
is accidental and should not be relied on.

On Sun, Dec 2, 2012 at 7:50 PM, jim <jim at well.com> wrote:

>     You probably tried using the  nice  command,
> maybe with most processes +10 and with -10 for
> your music processes, yes?
> On Sun, 2012-12-02 at 13:00 -0800, Ken Restivo wrote:
> > OK, I know I've been using Linux audio for 6 years now, and gigged and
> recorded with it extensively for most of those, yadda yadda. But it seems
> I've had an embarassingly huge hole in my knowledge the whole time.
> >
> > I was under the impression that, in order to use real time
> priorities/permissions and Ingo kernels, it was required for the process
> ITSELF early in the main() routine of its source code, to make some system
> calls to claim RT priority. In fact, I specifically remember reading or
> even writing source code in C which did that (probably based on JACK sample
> code). I don't recall the name of the syscall, but it was something obvious
> and well-documented.
> >
> > Also, I remember that it was also required that the software behave
> properly in order to be real-time capable, something about callbacks taking
> some predictable amount of time. Or perhaps that was only a JACK
> requirement.
> >
> > Why am I asking these dumb-ass questions now? Because I've been playing
> around with Liquidsoap and Airtime for some radio stations, and I'm
> obsessed with getting them as rock-solid on cheap/free/old hardware as I'd
> been able to get with my gigging and studio synths.
> >
> > It physically pains me to hear audio stuttering because Apache is
> running on the same box. It seems an outrage to me. Shouldn't happen. Ever.
> I used to record and mix multi-track songs in Ardour with tons of
> single glitch. I expect no less.
> >
> > So I asked on the Liquidsoap list, and I got only shrugs and a pointer
> to the Gentoo page in response (why? I have no idea. I use Debian, and
> that's irrelevant to the question at hand anyway.).
> >
> > So what's the deal? Is there a way to give Ingo-approved preemptive RT
> priority to things that aren't real-time apps and aren't specifically
> architected for that? What, if anything, would break?
> >
> > And, if I wanted to hack Liquidsoap (which would require learning ML,
> which wouldn't be a bad thing to know anyway), is it even possible to get
> it RT-capable, or are there low-level C system calls required in order to
> make that work?
> >
> > Sorry for the long and obscure question, but it's been bothering me for
> a while, and I figured someone here would know the answer, or where I might
> find it.
> >
> > Thanks.
> >
> >
> > -ken
> > _______________________________________________
> > Linux-audio-user mailing list
> > Linux-audio-user at lists.linuxaudio.org
> > http://lists.linuxaudio.org/listinfo/linux-audio-user
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