Ingo Molnar <[email protected]> writes:
> - if everything fails and automatic latency tracing does not show
> anything out of ordinary, then you could try to do "user-triggered
> tracing" of jackd's critical path. This is more laborous to do, but
> should pinpoint the latency reason in a pretty sure way.
>
> user-triggered tracing is done via adding those special gettimeofday
> calls to jackd and recompiling jackd. I've attached an older hack
> against jackd below, you might need to merge it to recent jackd. NOTE:
> this patch will only work if you are getting xrun messages from ALSA.
> It has to be reworked if your latencies are not actual xruns.
JACK sources already include a CHECK_PREEMPTION() macro which expands
to Ingo's special gettimeofday() calls. The trace is turned on and
then off automatically before and after the realtime critical section
in the process thread (see libjack/client.c).
Ingo's suggested ALSA backend patch is not presently included.
There are probably some other places where these macros could usefully
be added. We will integrate patches adding them in appropriate spots.
They do no harm in vanilla kernels without tracing enabled.
--
joq
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