Re: [LAU] A surprisingly stupid RT priority question

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To: Ken Restivo <ken@...>
Cc: linux-audio-user <linux-audio-user@...>
Date: Sunday, December 2, 2012 - 9:17 pm

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simple answer: non-RT things need more buffering between them and the
hardware. find out how to do that.

On Sun, Dec 2, 2012 at 4:00 PM, Ken Restivo wrote:

> OK, I know I've been using Linux audio for 6 years now, and gigged and

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simple answer: non-RT things need more buffering between them and the hardw=
are. find out how to do that.On Sun, Dec 2, 2012 at 4:00 PM, Ken Restivo <ken@resti=
vo.org
> wrote:
OK, I know I've been using Linux audio f=
or 6 years now, and gigged and recorded with it extensively for most of tho=
se, 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/permi=
ssions and Ingo kernels, it was required for the process ITSELF early in th=
e 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 c=
ode in C which did that (probably based on JACK sample code). I don't r=
ecall the name of the syscall, but it was something obvious and well-docume=
nted.

Also, I remember that it was also required that the software behave properl=
y in order to be real-time capable, something about callbacks taking some p=
redictable 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 ob=
sessed 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 o=
n the same box. It seems an outrage to me. Shouldn't happen. Ever. I us=
ed to record and mix multi-track songs in Ardour with tons of soft-synths W=
HILE A KERNEL COMPILE WAS GOING ON THE SAME MACHINE without a single glitch=
. I expect no less.

So I asked on the Liquidsoap list, and I got only shrugs and a pointer to t=
he Gentoo page in response (why? I have no idea. I use Debian, and that&#39=
;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 specifical=
ly 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 mak=
e 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 migh=
t find it.

Thanks.

-ken
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Messages in current thread:
[LAU] A surprisingly stupid RT priority question, Ken Restivo, (Sun Dec 2, 9:01 pm)
Re: [LAU] A surprisingly stupid RT priority question, Paul Coccoli, (Sat Dec 8, 7:20 pm)
Re: [LAU] A surprisingly stupid RT priority question, Pedro Lopez-Cabanillas, (Sun Dec 2, 10:04 pm)
Re: [LAU] A surprisingly stupid RT priority question, Ken Restivo, (Mon Dec 3, 2:27 am)
Re: [LAU] A surprisingly stupid RT priority question, Aaron Krister Johnson, (Mon Dec 3, 4:48 pm)
Re: [LAU] A surprisingly stupid RT priority question, Harry van Haaren, (Sun Dec 2, 9:23 pm)
Re: [LAU] A surprisingly stupid RT priority question, Paul Davis, (Sun Dec 2, 9:17 pm)