Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-6

[K.R. Foley]

Ingo Molnar wrote:
> * K.R. Foley <kr@xxxxxxxxxx> wrote:
>
>
> > running realfeel with rtc histogram generates > 100 usec entries in
> > the histogram but none of these are ever caught by the wakeup tracing.
>
>
> can you reproduce this with rtc_wakeup:
>
>   http://www.affenbande.org/~tapas/wiki/index.php?rtc_wakeup
>
> ?
>
>
> > I think I know why we don't get traces from this. TIF_NEED_RESCHED is
> > not set for IRQ 8 at the time that it wakes up realfeel so
> > _need_resched fails and trace_start_sched_wakeup doesn't actually call
> > __trace_start_sched_wakeup(p)???
>
>
> here's the code:
>
> +static inline void trace_start_sched_wakeup(task_t *p, runqueue_t *rq)
> +{
> +       if (TASK_PREEMPTS_CURR(p, rq) && (p != rq->curr) && _need_resched())
> +               __trace_start_sched_wakeup(p);
> +}
>
> indeed this only triggers if the woken up task has a higher priority
> than the waker... hm. Could you try to reverse the priorities of 
> realfeel and IRQ8, does that produce traces?

I guess I really am slow. You laid it all out for me above and I still 
didn't get it until I looked at again. I still haven't been able to 
capture an actual trace from any of these programs, but thanks to your 
addition of logging all of the max latencies in 32-14 I can see that the 
traces were there until another trace pushes them out.
> 	Ingo

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