[ardour-users] ok, spoke too soon... major crash w/ 0.9beta16.1

Fernando Pablo Lopez-Lezcano nando at ccrma.Stanford.EDU
Tue Jun 8 17:57:25 PDT 2004

On Tue, 2004-06-08 at 17:51, Joe Cooper wrote:
> Fernando Pablo Lopez-Lezcano wrote:
> > On Tue, 2004-06-08 at 17:03, Joe Cooper wrote:
> > 
> >>derek holzer wrote:
> >>
> >>>Just when I was getting to love it, Ardour froze up and made the machine 
> >>>totally unresponsive! Couldn't even ssh in to kill the process, had to 
> >>>reboot.
> >>
> >>It's worth pointing out here that a user level application, like ardour, 
> >>cannot bring down a system*. 
> > 
> > Any user application running threads with realtime scheduling can bring
> > down a system. That's the tradeoff of not having xruns...
> > 
> >>Only a system level bug can do that (or 
> >>hardware failure).  Ardour might tickle the bug, but if your system 
> >>crashed or froze while running Ardour then the kernel has a bug. 
> >>Possibly, since presumably you've never seen it outside of Ardour (or 
> >>you wouldn't be blaming Ardour) it is in the sound card driver you are 
> >>using.  Jack might also be to blame, since it usually runs with rt 
> >>priority, needs special privileges, and seems to interact more closely 
> >>with the kernel than most sound servers (I'm guessing--I don't know 
> >>where the user/system line is in the alsa/jack stack).
> > 
> > A thread running with realtime scheduling can completely hog the cpu of
> > a running system if it does not return control (ie: no other process
> > gets to run ever again). Jack has a watchdog timer designed to prevent
> > such a thing from happening, I guess it is not perfect. 
> I had no idea ardour inherited the realtime scheduling from Jack (at 
> least, I've never run ardour explicitly rt, though I do run jack with 
> rt).  Good to know.

Not all of ardour, just the audio thread. 

> That brings to mind the question: Does one have to explicitly run ardour 
> with rt to get realtime scheduling in ardour, and if so, how?  Running 
> jack with realtime scheduling is documented, but I don't recall ever 
> seeing anything about ardour and rt.  Perhaps I simply misunderstand how 
> tightly jack and ardour are coupled (this is not at all unlikely).

You do not need to do anything in ardour. If Jack is running with
SCHED_FIFO scheduling (realtime scheduling) and the kernel has the
capabilities patch (or for 2.6.x the realcap security module), the audio
threads of Jack clients will be run SCHED_FIFO as well. 

-- Fernando

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