[LAU] xrun killer: --sync on jack2

[Guru Prasad B. R.]

Thanks Jonathan for the heads up on Jack2!
A quick update:
If you remember form my earlier posts (re: Fluidsynth, soundfonts, jack, 
and latency), I'd devised a "stress test", with the following results: 
(a) stable with a 1.6 GB piano sample in linuxsampler (b) promptly crash 
with a 8.2Mb string  soundfont with any fluidsynth-based  application. 
By crash, I mean jack requiring a restart, making things unusable for 
live performance.

My strong suspicion was a bug with fluidsynth, to which I did receive 
helpful replies.

Subsequently, I came across ChickenSys Translator, which can convert a 
soundfont to a gigastudio sample. I converted the same 8.2 Mb string sf2 
to a gig, and guess what - now with the same stress test, linuxsampler 
crashes jack!

So the issue is not really with fluidsynth, but with jack itself. David 
had rightly suspected something to this effect, and Josh had suggested 
that Jack2 would be more resilient.

I now believe the improved performance in my stress test when I upgraded 
jack was due to switching from jack to jack2. My system has subsequently 
become much more stable. I now need to try out the --synch mode in jack2.

Quick question: How do I get into --synch mode using qjackctl?
Looking forward to inputs/suggestions.
Cheers,

Guru

[P.S. I hope I haven't hijacked the thread topic...]


Jonathan E. Brickman wrote:
> I think I've got it :-)  Muchas gracias to Joakim Hernberg, who posted 
> the jack2 profiling document.  I read it about five times, trying to 
> ponder what my first step might be given that info.  It discusses two 
> major modes of jack2:  the default, which is asynchronous, and another, 
> which is synchronous.  Under asynch, my stress-test yields zero xruns 
> (or close) at 5.3 ms (as reported in Qjackctl); but under synch, my last 
> two tests say kosher at 0.667 ms *grin*  Shocking.  That synch makes a 
> whole lot of difference.  I can just imagine jack2 jockeying all four 
> CPUs to make that happen :-)  I'll be doing a lot more stress-testing to 
> prove it, but for right now, frames/period are 64, sample rate 192000, 
> two periods/buffer :-) :-)  I praise the Lord, and I thank everyone for 
> the help!
>
> J.E.B.
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>   


-- 
Guru Prasad B.R.
Centre for Ecological Sciences 
Indian Institute of Science
Bangalore - 560 012
India
Ph:+91-80-22933103