Gilles Chanteperdrix wrote:

Philippe Gerum wrote:

On Thu, 2007-05-03 at 17:07 +0200, Gilles Chanteperdrix wrote:

That was not my point. My point was: don't stuff huge semi-random values
into /proc/xenomai/latency to work around terrible jittery especially
when porting Xenomai over new platforms, because this is _likely_ the
sign of something going wrong elsewhere.

E.g. An oldish 90Mhz classic pentium exhibits ~25 us core latency
figures with Xenomai; some ARM hw may require more because of
unfortunate memory sub-systems, but in any case, you have to
_understand_ (e.g. using the tracer) why it is so, first.


I agree. I still have to see for myself why these damned ARMs have such
high latencies.

Big LDM/STMs with slow memory will do the trick every time. The CSB637 has a 100 MHz memory bus, even though the CPU can run at almost 200 MHz.

I think the cache and MMU arrangements have implications, too. And anything tied to NWAIT on that chip (AT91RM9200) drags the system down quite easily.

Don't accept those explanations at face value, though. I'd love to see the root cause clearly identified.

b.g.

-- 
Bill Gatliff
bgat@domain.hid