On Thursday 30 November 2006 14:48, Markus Franke wrote: > Ulrich Schwab wrote: > > I think that CONFIG_PREEMPT should reduce the jitter of Your measurement, > > most importantly the worst case switch time, for wich You need a long > > test run under heavy load. > > CONFIG_PREEMPT is there to provide more determinism, which usually has a > > price in performance. > > Realtime is about determinism not performance (or speed). > > Its not maximum speed but guaranteed minimum speed. > > You are absolutely right. I put my system under some load (dd) and made > two tests. One was with CONFIG_PREEMPT and one without. The worst case > switch time jitter was about 30% lower in the CONFIG_PREEMPT case, so > your prediction was right. > > > Since the probability of a preemption during the mode switch without > > CONFIG_PREEMPT is lower, it might take a long time until the worst case > > mode switch time is observed. > > Sorry but I don't understand what you are meaning. Let me explain my > point of view. When a realtime task in the Xenomai-Domain makes a > linux-systemcall the task is migrated fully automatically to the > Linux-Domain as soon as we reach the next preemption point in the > Linux-Kernel. Due to the fact that preemptability of the linux-kernel > increase when using CONFIG_PREEMPT, the time to the next preemption > point should decrease, right? Correct. But I wrote: " without CONFIG_PREEMPT " meaning: the time to the next preemption point is bigger, which might get the requested system call done before the preemption is actually happening.
> I don't get the point of your last sentence. Ulrich -- ==================================================== inmess GmbH Frankfurter Str. 74 D - 64521 Gross-Gerau Phone: +49 6152 97790 Fax : +49 6152 977920 mail : [EMAIL PROTECTED] web: www.inmess.de ==================================================== _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
