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

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

Disabling the I- or D-cache is available as an option by using
menuconfig under system-type.

As to the Jitters - I didn't describe it correctly what i was doing. I
disabled the both caches as a trick to test if there is a difference.
The 2 us timing difference was without the caches. With I- and D-cache
online i had a difference of 13 us as average value (15us idle and 3 us
with user space load)

I have to estimate a critical path in order to decide if a timer
interrupt driven periodic task or a xenomai periodic task is better for
my system. As I noticed this effect of the idle task I had to know why
in order to document it or to change the part of the code.

Well, now I know what to do and I have to find out if disabling the
I-cache is critical at this point and if so, how one can avoid it. My
system doesn't have  to save power if its online and I suppose that
disabling this kind of idleness could be a nice feature in the kernel or
xenomai.

So thank you for your help again and have a nice weekend,

Best regards,
Karl Tyss
 

Mit Freundlichen Grüßen,
Karl Tyss



>>> Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org> 06/05/09
4:17 PM >>> 
Karl Tyss wrote:
> 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.

Also, let me insist: 2 microseconds on ARM is peanuts. Really, it is
insignificant, you will get much worse jitters than that with a
properly
loaded system.

-- 
					    Gilles.



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