On Wednesday 02 December 2009 11:09:18 fons(a)kokkinizita.net wrote:
  In theory zita-convolver could be modified quite
easily
 to work correclty in freewheeling even on MP systems.
 The complicated part is switching between normal mode
 and freewheeling 'on the fly' - I've not worked out
 how to do that correctly.
 But as said, on a single processor system it will work.
 What is happening is this: zita convolver uses some
 processing threads that effectively run with a period
 that is a power-of-2 multiple of Jack's basic period.
 They run on RT priorities just below the one of Jack's
 process thread (-1 for for each doubling of the period).
 The output of these threads must be ready when their
 next period starts.
 Zita-convolver checks this condition and will report
 errors if these threads are too slow, but it will not
 wait for them - you're not supposed to wait in Jack's
 callback, and if your system does support the CPU load
 for the given configuration they will be ready, even
 with some safety margin.
 When freewheeling, Jack's main process thread will be
 non-RT, while these extra threads remain at RT. So
 they will pre-empts Jack's thread and will appear to
 be always ready on time. Except when you have 2 CPUs:
 then Jack's thread will be allowed to continue even
 if some of the others have not yet completed their
 work. 
Wouldn't the easiest solution be to wait for the worker-threads when in
freewheeling mode?
If I understand it correctly, it isn't "no waiting in jack-callback" but
"no
waiting in realtime threads". Afaik freewheeling means to run as fast as
possible but let all clients do their work. So waiting for slave threads
should be okay then.
Arnold