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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8

* Florian Schmidt <mista.tapas@gmx.net> wrote:

> i just wanted to let you know that with U8 i still experience the
> "pauses" i reported on U6, too. I would guess that it's some scheduler
> thing as jackd running SCHED_FIFO and all its clients (at least the
> audio threads running SCHED_FIFO) are not affected by the pauses (i
> don't see any xruns from jackd and audio processing happily goes along
> without audible dropouts).

ok.

> Also it seems that /proc/sys/kernel/trace_enabled == 1 is not the only
> thing being able to trigger the pauses. With U6 i also experienced
> them with trace_enabled == 0. I have to add though that it took quite
> a while for them to kick in (hours) after setting trace_enabled to 0.
> So my conclusion is that trace_enabled == 1 just increases the
> probability of such pauses by several magnitudes (with 1 i get about
> one of these pauses per 2-10 minutes, with 0 it took several hours for
> the first pause to occur and then they stayed less frequent than with
> 1).

i dont think it's caused by trace_enabled - the trace you sent last time
clearly showed erratic behavior. There's one piece of code i suspect in
particular - could you try the patch below ontop of -U8? (i have
compile- and boot- tested it)

Ingo

--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -2764,6 +2764,8 @@ need_resched:
else
deactivate_task(prev, rq);
}
+ if (preempt_count() & PREEMPT_ACTIVE)
+ sub_preempt_count(PREEMPT_ACTIVE);
if (unlikely(prev->flags & PF_DEAD)) {
BUG_ON(prev->state != TASK_RUNNING);
prev->state = __TASK_DEAD;
@@ -2940,6 +2942,7 @@ asmlinkage void __sched preempt_schedule
return;

need_resched:
+ local_irq_disable();
add_preempt_count(PREEMPT_ACTIVE);
/*
* We keep the big kernel semaphore locked, but we
@@ -2950,11 +2953,10 @@ need_resched:
saved_lock_depth = task->lock_depth;
task->lock_depth = -1;
#endif
- schedule();
+ __schedule();
#ifdef CONFIG_PREEMPT_BKL
task->lock_depth = saved_lock_depth;
#endif
- sub_preempt_count(PREEMPT_ACTIVE);

/* we could miss a preemption opportunity between schedule and now */
barrier();
@@ -3002,7 +3004,6 @@ need_resched:
#ifdef CONFIG_PREEMPT_BKL
task->lock_depth = saved_lock_depth;
#endif
- sub_preempt_count(PREEMPT_ACTIVE);

/* we could miss a preemption opportunity between schedule and now */
barrier();
@@ -3842,9 +3843,9 @@ static inline void __cond_resched(void)
if (preempt_count() & PREEMPT_ACTIVE)
return;
do {
+ local_irq_disable();
add_preempt_count(PREEMPT_ACTIVE);
- schedule();
- sub_preempt_count(PREEMPT_ACTIVE);
+ __schedule();
} while (need_resched());
}

-
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