Andreas Glatz wrote:
> Hi,
>
> On Thu, Apr 15, 2010 at 06:46:58AM -0400, Philippe Gerum wrote:
>> On Wed, 2010-04-14 at 20:19 -0400, Andreas Glatz wrote:
>>
>>> One thing I've noticed though, and this is not related to the patch (I
>>> verified it on a
>>> vanilla Xenomai system): Consider the example I included. It prints average
>>> cycle times
>>> and the cycle time variance of the high priority task ("T2"). I noticed a
>>> big difference
>>> in the cycle time variance when switching the first task ("T1") to
>>> secondary mode with
>>> rt_task_set_mode() and setting the scheduler policy to either SCHED_FIFO,
>>> SCHED_IDLE or
>>> SCHED_NORMAL. I'm assuming someone asked this before and I didn't pay
>>> attention :)
>>> Can someone give me a short explanation or point me somewhere to get an
>>> explanation for
>>> this behaviour? I didn't expect such a difference in variance:
>>>
>> Moving back to secondary mode is nothing more than triggering the
>> rescheduling procedure linux-wise, so the time credit for
>> SCHED_OTHER/IDLE tasks decay as usual during your work loop, preemption
>> by high priority task is more likely and so on. This variance is just
>> the sign that those tasks cannot ask for more than what their scheduling
>> policy grants.
>>
>
> I think, I didn't express myself clearly enough. I was more puzzled about
> the variance of the pure RT task (task w/o any secondary mode switches).
> So it seems that changing the scheduling policy of the "relaxed" task has
> an influence on the variance of the pure RT task. So the RT task seems
> to wait for the "relaxed" task. But where exacly does it wait for it? Mmmmm...
When waiting for the mutex?
--
Gilles.
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