Re: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0

[Ingo Molnar]

* Florian Schmidt <mista.tapas@xxxxxxx> wrote:

> 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

just curious, are these two important to the latency path of jackd, or
are they lowprio things and are thus at SCHED_OTHER intentionally?

> ~$ 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.

yeah, i'm hunting a quite similar bug: i can see 'realfeel' latencies
generated by simple window scrolling. It is most likely a logic bug
somewhere - a missing reschedule check, irqs left disabled accidentally,
or something like that. Since some other workloads dont trigger it i
dont think i broke RT scheduling by itself - it is most likely some
non-core code somewhere missing a resched. Which doesnt make it less of
a problem, but it makes it harder to find :-|

	Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/