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

Fernando Lopez-Lezcano wrote:

>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
>
>
>
>
Aaaaah! I see! Yes, I was starting jackd with the -R flag... but I
didn't know jackd had more than one thread running at the same time.
This is what I get:

hector@email-addr-hidden:~$ for pid in `ls /proc/8260/task/` ; do chrt -p $pid ; done
pid 8260's current scheduling policy: SCHED_OTHER
pid 8260's current scheduling priority: 0
pid 8261's current scheduling policy: SCHED_OTHER
pid 8261's current scheduling priority: 0
pid 8262's current scheduling policy: SCHED_FIFO
pid 8262's current scheduling priority: 80
pid 8263's current scheduling policy: SCHED_FIFO
pid 8263's current scheduling priority: 70

Thank you Fernando and Florian.

Hector.
Received on Sun Feb 26 20:21:29 2006