Re: [linux-audio-user] jackd and realtime priority

On Sat, 2006-02-25 at 02:44 -0500, Hector Centeno-Garcia wrote:
> Hi,
>
> I've been playing around a little with the priority thing. I would like
> to understand better the way it works. Looking at the priority of jackd
> (running realtime, as user, and with a RT kernel, full-preemption) I
> can't figure out why if I start jackd with -P 60 (or any other number >
> 0) the output of chrt is always:
>
> $ chrt -p (jackd's pid)
> pid 8115's current scheduling policy: SCHED_OTHER
> pid 8115's current scheduling priority: 0
>
> I checked this in two different distros (FC4+CCRMA and Ubuntu with
> custom RT kernel) and the result is the same. Is it not supposed to read:
>
> $ chrt -p 8115
> pid 8115's current scheduling policy: SCHED_FIFO (maybe?)
> pid 8115's current scheduling priority: 60
>
> I know that I can set this manually, but I'm just wondering what is the
> real effect of the -P flag.
>
> Any help will be appreciated,

Assuming you did start Jack with the "-R" option you are probablyk
looking at the main Jack process and that is actually SCHED_OTHER. Jack
has more threads and some of them are SCHED_FIFO.

Do this:
  ls /proc/(jack's pid)/tasks
and you will see the pids of the other threads (I'm sure there must be a
more elegant way of finding this info)

A chrt of those will show something like this:

$ for pid in `ls /proc/27701/task/` ; do chrt -p $pid ; done
pid 27701's current scheduling policy: SCHED_OTHER
pid 27701's current scheduling priority: 0
pid 27702's current scheduling policy: SCHED_OTHER
pid 27702's current scheduling priority: 0
pid 27703's current scheduling policy: SCHED_OTHER
pid 27703's current scheduling priority: 0
pid 27704's current scheduling policy: SCHED_FIFO
pid 27704's current scheduling priority: 72
pid 27705's current scheduling policy: SCHED_FIFO
pid 27705's current scheduling priority: 62

And there you have the rt threads...
-- Fernando
Received on Sun Feb 26 20:21:29 2006