[linux-audio-user] jack.plumbing segfault

Ken Restivo ken at restivo.org
Sun Jan 14 01:36:38 EST 2007

Hash: SHA1

On Sat, Jan 13, 2007 at 09:52:32PM -0500, carmen wrote:
> On Sat Jan 13, 2007 at 06:42:16PM -0800, Ken Restivo wrote:
> > jack.plumbing is giving me segfaults shortly after launch.
> > 
> > I've attached an strace. I got no backtrace in gdb, usually don't with SIGSEGV's anyway. And I dunno how useful it would be to run a process that talks to jack (realtime, low-latency) under GDB anyway.
> > 
> > My .jack.plumbing is also attached just for fun.
> you should proably email Rohan Drape
> i like jack.plumbing in concept. but its saddled by a number of issues - first the tarball is almost impossible to track down (the slavepianos site seems to be up recently though, so maybe you can find it on there), it segfaults, and doesnt actually 'plumb'. at least for me
> it would be great to see it fixed. does anything else do plumbing besides QcrapCTL?

Well this is very bizarre.

First of all, I *like* jack.plumbing. It worked for me up until recently, and I've been trying to figure out WTF happened.

So far, the answer appears to be:

- -P 60

I'm not kidding.

Starting jackd with -P 80 causes two things to break:

	1) Rosegarden slows my softsynths down to a crawl, such that whenever jack transport is running, my latency for softsynths gets noticeably (and unusably) worse. So I took Rosegarden out of the loop, and, sure enough, if I connect my USB keyboard directly to the softsynth, latency is fine. If I connect it through Rosegarden (which I need to do in order to record), then it lags.

	2) That appears to have been causing jack.plumbing to segfault! If I bring jackd back to -P 60, jack.plumbing works again.

Any ideas what's going on here? Only thing I can guess is that the -P setting doesn't apply to all realtime applications, only to jackd itself. So, with it set too high, programs like rosegarden or jack.plumbing get starved for resources.

Another possibility is that my recent use of rtirq may be a factor. Maybe the alsa MIDI driver is getting starved and is too low priority, and jack is grabbing all the resources.

What I'm worried about is the possibility of getting Xruns when running Ardour now, which is why I started messing with this.

I hope I'm wrong, but it seems like ardour, rosegarden, alsa, freebob, and softsynhs, are all competing for resources and do not play well together-- if I make one happy, one or more of the others start breaking. 


- -ken
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