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
> 
> ?

Yes. See attached files. When I ran rtc_wakeup the priorities were
IRQ 8= 97
IRQ 0= 96
Dropping IRQ 8 (down to 86) below rtc_wakeup kept rtc_wakeup from 
completing any runs.

> 
> 
>>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);
> +}

I know. I MUST KEEP MY MOUTH SHUT. I MUST KEEP MY MOUTH SHUT. I just 
didn't see how it was possible that either of the other two conditions 
could ever be false in this case and I missed the call to resched_task
> 
> 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 did this and latencies in the histogram dropped drastically. The 
highest latency in the histogram is 33 usecs and thus never gets high 
enough to trigger the tracing???

IRQ 8 = 97
IRQ 0 = 96
realfeel = 98


> 
> 	Ingo
>