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

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

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.