Messages in this thread |  | | | Date | Thu, 2 Dec 2004 09:40:40 +0100 | | From | Ingo Molnar <> | | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.31-19 |
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* Florian Schmidt <mista.tapas@gmx.net> wrote:
> On Wed, 1 Dec 2004 23:09:16 +0100 > Ingo Molnar <mingo@elte.hu> wrote: > > > but ... this brings up the question, is this a valid scenario? How can > > jackd block on clients for so long? Perhaps this means that every audio > > buffer has run empty and jackd desperately needed some new audio input, > > which it didnt get from the clients, up until after the xrun? In theory > > this should only be possible if there's CPU saturation (that's why i > > asked about how much CPU% time there was in use). > > > > One indication that this might have been the case is that in the full > > 3.5 msecs trace there's not a single cycle spent idle. But, lots of time > > was spent by e.g. X or gkrellm-4356, which are not RT tasks - so from > > the RT task POV i think there were cycles left to be utilized. Could > > this be a client bug? That seems a bit unlikely because to let jackd > > 'run empty', each and every client would have to starve it, correct? > > actually a single client doing nasty (non RT) stuff in its process() > callback can "starve" jackd. AFAIK jackd waits until the last client > has finished its process callback. So, if some client's process > callback decides to use (for example) some blocking system call (big > no no) and consequently falls asleep for a relatively long time, then > it can cause jackd to miss its deadline. I'm not sure though wether > this triggers an xrun in jackd or just a delay exceeded message.
since the period size in Rui's test is so small (-p64 is 1.6 msecs?), the 2.6 msec timeout in pipe_poll() already generates an xrun.
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