[LAU] Linuxsampler says: " Thread: WARNING, can't assign realtime scheduling to thread!"

[Guru Prasad B. R.]

Hello everyone,
  I'm running Ubuntu Jaunty 9.04 (on a different laptop, not the one 
running AVLinux). Till recently, my linuxsampler setup on this 
particular system was working without (major, noticable) glitches, i.e 
very few xruns and not many dropped notes. Since the past few days, 
however, I'm seeing a host of xruns and buzzes and drop notes. I tried 
switching to the RT kernel (kernel 2.6.28-3-rt, via synaptic). The 
result - a *huge*, unmanageable latency. I also noticed this warning 
which I'd not seen before:


Thread: WARNING, can't assign realtime scheduling to thread!


I'm using jackdmp 1.9.4, compiled from source:

/usr/local/bin/jackd -S -R -dalsa -dhw:0 -r44100 -p256 -n2


I'm sure there are better realtime kernels out there, but before I 
switch the kernel, I'd like to understand why exactly linuxsampler is 
not being allocated realtime priority. I don't know much about this.
Incidentally, here's what 'top' reveals: (Note: these are with the 
vanilla kernel).

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  
COMMAND           
29516 guru      20   0 35872  13m  10m R 10.3  1.4   0:28.17 
qsampler          
29503 guru      20   0  437m 436m  76m S  2.7 46.5   0:11.57 
linuxsampler      
29493 guru      20   0 88632  74m  72m S  2.3  8.0   0:11.20 
jackd             

No user-owned entries have RT priority, but down the list some 
root-owned processes do, for e.g:
3 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 migration/0
All user-oned processes have the same priority: 20
My /etc/security/limits.conf file ends with this:
@audio   -  rtprio     19
@audio   -  memlock    unlimited
@audio   -  nice      -19
 And I'm a member of the group 'audio'.

Can someone help me out with this?
Thanks in advance!
Cheers,

Guru




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