[Jack-Devel] Profiling xruns

Hi!

I am developing a jack client that is handling different input devices
(like joysticks, touch screens, etc.) and capable of using them as
musical input devices.

The architecture is relatively simple: A directed acyclic graph can be
made up of different boxes, each of them performing different tasks, 
like
reading input, generating oscilating values, passing data to a jack 
midi
or audio port, etc. When the graph is modified, a non-rt thread 
generates
a topologic ordering of the nodes into a linked list and a pointer to 
the head
is passed in a ringbuffer to the process function which at its 
beginning examines
the content of the buffer and can store the new list. In each process
call, the list is iterated and the process function is called for each 
box.
The edges have buffers which are read and written by the boxes and the 
topologic
ordering ensures that only those edges are read in a cycle whose data 
are
already computed.

The problem is: Even without having ANY nodes, thus the process 
function doing
practically nothing, sometimes the application does xruns. I am sure 
that the
source of these xruns is the application as they show up in the 
messages
window of qjackctl with the app's name. Also, I am running in soft 
mode, which
I assume, means that xruns indicating that the backend is not fast 
enough, are
ignored.

How could I locate the cause of these xruns? Is there a good practice 
for profiling
these problems? I think it is hard because using tools like gprof will 
make the
app slow and cause xruns which would never occur without the profiling 
itself.

I am using mlockall and a big memory pool, a thread pool (though 
currently no threads
are created when process is called), process shielding for the sound 
card soft irq,
jackd and the app.

Jack settings: Rt priority 83, Frames/Period: 128, Sample rate: 48000, 
Periods/Buffer: 2.
The latency is 5.33 msec and apps like ardour xrun only very rarely, 
under heavy usage.
The machine is a samsung notebook with a core i3 cpu, 3Gb ram and 
unfortunately an onboard
soundcard.

Is it better for xrun debugging to use the dummy interface in order to 
be totally
independent of the sound card? Also, could it be the problem that I am 
using
clutter for gui? I am quite a beginner in developing audio 
applications...

Thank you in advance,
Dennis

1332031366.26680_0.ltw:2,a <dc0dcd2dbc3d7fa20727ac57a325dd8c at rudanium dot org>