Re: [Xenomai-help] IRQ-Latency when in idle State on ARM

["Karl Tyss" <tyss.k@domain.hid>]

Hi,

5 minutes ago I found out that one of the caches definately has to
cause the problem. I believe I would have to spent couple of more days
to find out why. 

Your hint was a bulls eye. I tried a dirty trick and commented out the
two lines responsible for disabling the I-cache.  It helped. I wonder if
it leads to other problems. I will test it and post my results.

Thank you both for the quick and productive help.

Best regards,
Karl Tyss
 

Mit Freundlichen Grüßen,
Karl Tyss



>>> Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org> 06/05/09
3:42 PM >>> 
Karl Tyss wrote:
> Hi,
> 
> thank you for the quick answer.
> 
> The idea with deactivating the caches is to see if they are
influencing
> this behavior. I also tried out the FCSE option and it did not help.
My
> issue is that if there is a user space application that starts lots
of
> short processes/threads and sleeps for a short time, in this case I
get
> a large jitter. Till this point I was able to find out that it makes
a
> difference if the idle task is running. 
> 
> These simple tests I was running weren't supposed to be relevant
stress
> tests. I only tried to prevent the kernel entering the idle task and
the
> simplest way was to start an endless loop doing noting.
> 
> So my question was actually is there any explanation to this
behavior
> and in both cases (yes or no) is this behavior predictable? Perhaps
one
> can avoid this by modifying the cpu_idle task, so that the system
> doesn't necessarily go in a sleep mode.

Ok. If I understand correctly, the AT91SAM9G20 uses an arm926ejs core,
and in arch/arm/mm/proc-arm926.S, the idle function disables and
re-enables the I-cache, so, that may be the source of your problems.

-- 
					    Gilles.



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