29 Jun
2019
29 Jun
'19
9:42 a.m.
On Sat, Jun 29, 2019 at 2:54 PM Johannes Lorenz <j.spam(a)lorenz-ho.me> wrote:
Hello,
we run a DAW (LMMS) with jack and would like to exploit multiple cores.
Currently, we have one jack process (using `jack_set_process_callback`)
and multiple other processes that share all the work. The problem is
that only the jack process has RT prio. Imagine the following example:
* 4 threads, of which one is the jack thread, 3 have lower priority
* 4 tasks (e.g. 4 instruments play one note each)
* the realtime process is finished quickly, the other threads get
preempted by the kernel
These are situations where using such non-realtime helper threads can
threaten realtime behaviour. What is the best practice?
* Is it possible/good to use multiple rtprio threads controlled by jack?
(multiple clients, or multiple threads in one client)
I'm not sure what the problem is...
Are you asking if all your threads can call jack_ functions? There are
some jack functions (jack_get_time I think) that can be called from a
different thread, but this is explicitly documented for each function.
If not, it's probably safe to assume that you can't call a jack_
function from a non-jack thread.
* Should we keep using our non-rt helper threads?
Probably...
* Should we be single-threaded, to have a (probably)
longer average
time, but a better worst-case time?
Probably not...
* Should we start with helper threads and only the
last few jobs will
only be run by the realtime thread (to avoid problems like in the
example)?
In this scenario, is the realtime thread waiting for a non-realtime
thread? Then the answer is no. ;-)