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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0
On Wed, 27 Oct 2004 11:06:20 +0200
Ingo Molnar <mingo@elte.hu> wrote:

>
> * Ingo Molnar <mingo@elte.hu> wrote:
>
> > third time lucky?
>
> there was one more piece missing...
>
> i've also uploaded -RT-V0.3.2 with this fix included.

Hi,

V0.3.2 builds and boots fine here. It seems to run ok, too. Uptime 25
minutes and no BUG's [yay! 25 minutes already! ;)]. Well anyways,
preempt_max_thresh is at 38us after running several concurrent find's plus
jackd.

There's a problem though with jackd performance. Read on below if it is of
any interest at this point.

Soundcard IRQ is 3:

mango:~# cat /proc/interrupts
CPU0
0: 1331024 XT-PIC timer 0/31024
1: 3494 XT-PIC i8042 0/3494
2: 0 XT-PIC cascade 0/0
3: 781428 XT-PIC CS46XX 0/81428
5: 1811 XT-PIC eth0 0/1811
8: 4 XT-PIC rtc 0/4
12: 71236 XT-PIC i8042 1/71236
14: 5163 XT-PIC ide0 0/5163
15: 50392 XT-PIC ide1 0/50392
NMI: 0
ERR: 0

I set the irq handler thread to prio 99:

mango:~# chrt -p `pidof "IRQ 3"`
pid 118's current scheduling policy: SCHED_FIFO
pid 118's current scheduling priority: 99

jackd runs with a period size of 128 frames (48000hz samplerate) and with
SCHED_FIFO with prios from 60 to 70 (ps output is somewhat broken):

mango:~# ps -cmL `pidof jackd`
PID LWP CLS PRI TTY STAT TIME COMMAND
1286 - - - ? - 0:28 /usr/bin/jackd -R -P60 -t20000 -dalsa -
- 1286 TS 20 - SLsl 0:00 -
- 1287 TS 23 - SLsl 0:00 -
- 1288 FF 110 - SLsl 0:00 -
- 1289 FF 100 - SLsl 0:27 -

~$ chrt -p 1286
pid 1286's current scheduling policy: SCHED_OTHER
pid 1286's current scheduling priority: 0
~$ chrt -p 1287
pid 1287's current scheduling policy: SCHED_OTHER
pid 1287's current scheduling priority: 0
~$ chrt -p 1288
pid 1288's current scheduling policy: SCHED_FIFO
pid 1288's current scheduling priority: 70
~$ chrt -p 1289
pid 1289's current scheduling policy: SCHED_FIFO
pid 1289's current scheduling priority: 60

Anyways i get xruns like crazy under load (like 200 in 10 minutes). It seems
the scheduling class and high priority don't matter really as wiggling
windows around on the screen or doing a "find /" can easily provoke xruns.

flo
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