Re: [Xenomai-help] Will Linux kernel lose timer ticks when RT thread is running

[Philippe Gerum <rpm@xenomai.org>]

Li Yi wrote:
> Thanks for the clarification.
>  
> I added a sleep(1) before read the "/proc/interrupts", and the timer
> interrupts for Linux kernel really got "Replayed". The system time
> catches up with the wall clock.
> 
> But still some question:
> 
> On Thu, 2006-04-20 at 10:19 +0200, Philippe Gerum wrote:
> 
> 
>>>In the particular case of multi-ms processing, I would likely suggest to
>>>move it to a thread running in secondary mode without interrupt
>>>shielding, so that Linux asynchronous activities such as interrupt
>>>handling would still be possible, at the expense of a lesser execution
>>>time predictability of such processing though.
>>>
>>>
> 
> 
> In my test, I am using rt_timer_spin() to simulate the real-time
> workload. And "/proc/xenomai/stat" shows "MSW" as "1/1", and in one test
> loop, there is no change for "MSW". So I concluded my test case is
> running in secondary mode. And my "Interrupt shield support"
> configuration is _not_ select. But it looks the Linux kernel does _not_
> handle timer interrupt while the real-time task is running. Did I miss
> anything? 
>

rt_timer_spin() is a busy-waiting service, and your measurement task 
never relinquishes the CPU while processing. I would bet that you set up 
a very high (maximum?) SCHED_FIFO priority to the Xenomai task, which 
did not allow the IRQ thread to run.

i.e. On the Blackfin architecture, Adeos scales the IRQ thread priority 
from SCHED_FIFO(50) to SCHED_FIFO(50 + (IVG13-IVG7)), which would have a 
lesser priority than anything above SCHED_FIFO(56).

> 
> 
>>>You may want to make your measurement thread sleep() for a while before
>>>looking at the final tick counter; this would make sure that the IRQ
>>>threads have been given enough time to catch up and process all pending
>>>ticks they have in their log. Btw, did you activate CONFIG_PREEMPT?
>>>
>>
>>Er, sorry. There's no CONFIG_PREEMPT on Blackfin yet.
> 
> 
> 
> Thanks,
> 
> -Li Yi (Adam)
> 


-- 

Philippe.