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

["K.R. Foley" <kr@cybsft.com>]

Ingo Molnar wrote:
> * K.R. Foley <kr@cybsft.com> 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
>