On Thu, 2007-05-03 at 18:44 +0200, 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. >
Stelian might jump in as well, but IIRC, a problem we saw on the Integrator was due to the cost of TLB flushing upon switch_mm with hw interrupts off. As a consequence of this, even regular Linux operations would induce jittery for the real-time domain, since enabling hw interrupts while invalidating is a no-go (actually, it's a go, even a jump, but out of the window, to be precise...). > > >>We should add a page on the wiki about the latency calibration. > >> > > > > > > We should also provide an external tool for determining the most > > appropriate latency for a given workload / configuration. > > The latency tool already does a great deal of this job. > I was rather thinking of a tool that could explicitely search for and approximate the best value for calibration, not something only providing hints for that purpose. -- Philippe. _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
