[ardour-users] mysterious xrun phenomenon

[Jonathan Murphy]

Hi Folks,

I'm working on a project that has 9 tracks (8 stereo 1 mono). It's
twelve minutes long. At the 6 minute mark (exactly halfway through the
piece) during playback there's a massive slew of xruns and ardour
tries to wade through the mud until I stop it. This is what top is 
showing immediately after this happens.

top - 14:49:27 up  2:23,  1 user,  load average: 0.55, 0.52, 0.97
Tasks:  66 total,   3 running,  58 sleeping,   0 stopped,   5 zombie
Cpu(s): 46.6% us,  9.8% sy,  0.0% ni, 31.8% id, 11.8% wa,  0.0% hi,  0.0% si
Mem:    969440k total,   956476k used,    12964k free,     1376k buffers
Swap:   979956k total,       52k used,   979904k free,   759652k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND              
11546 root      16   0  118m 117m  20m R 46.8 12.4   2:10.54 ardour                
 7581 root     -40  -5     0    0    0 S  5.0  0.0   4:38.54 IRQ 5                 
11540 root      20   0 35692  34m 2512 S  2.3  3.7   0:11.96 jackd                 
 3258 root      14  -1 93308  12m 3972 S  1.3  1.3   5:34.84 X                     
11206 root      16   0  1988 1016  788 R  0.7  0.1   0:02.95 top                   
    3 root      -2   0     0    0    0 S  0.3  0.0   0:04.09 softirq-timer/0       
  810 root     -45  -5     0    0    0 S  0.3  0.0   0:03.17 IRQ 14                
 7847 root      16   0  7376 2372 1688 R  0.3  0.2   0:18.80 aterm                 
11538 root      15   0 28960  28m  17m S  0.3  3.0   0:04.93 qjackctl              
    1 root      16   0  1508  516  452 S  0.0  0.1   0:00.29 init                  
    2 root      -2   0     0    0    0 S  0.0  0.0   0:00.09 softirq-high/0        
    4 root      -2   0     0    0    0 S  0.0  0.0   0:00.00 softirq-net-tx/       
    5 root      -2   0     0    0    0 S  0.0  0.0   0:00.26 softirq-net-rx/       
    6 root      -2   0     0    0    0 S  0.0  0.0   0:00.00 softirq-scsi/0

I'm running linux 2.6.15.4 with mingo's realtime-preempt patches 
(patch-2.6.15-rt16), jackd version 0.100.0 tmpdir /mnt/ramfs protocol
15, alsa 1.0.10, Ardour/GTK 0.99.1 (built using 1.2.1 with libardour
0.904.1 and GCC version 3.4.3). 

No other applications cause this kind of behaviour for me. I upgraded
to ardour 0.99.1 today to see if that would fix things. While
building ardour, I was watching a dvd using mplayer, sound output
through jack. To try to push things a bit (trying to force a similar
xrun situation), I opened up jack-rack and set up a chain of half a
dozen ladspa plugins processing the sound from the dvd: canyon delay,
stereo reverb and so on. No xruns. I started up fluidsynth, loaded a
bloated GM sf and plugged it into reverbed. No xruns. Opened up
firefox and started surfing ... No xruns, all four fluxbox desktops
full of the greediest apps I could find.

Is anyone else getting this kind of weird behaviour from ardour? I
have a hunch that ardour is unable to use swap space for some reason,
but this is just a guess. The 52k swap space that top shows was used
by mplayer during the gruesome frolic described above. 

Any ideas?

Jonathan.