On Fri, Aug 20, 2004 at 09:08:25PM +0200, Marc Kleine-Budde wrote: > > > Conclusion: As ''slow'' as the the last tests, but we can guarantee a > > > upper limit (about 115 us) but that's not the point.
> > I think we already mentioned it, but the figures you are comparing are : > > RTAI/LXRT, sampling period: 100us, jitter 40us > > RTAI/fusion, sampling period: 1ms, jitter 100us > Yes - I remember that :) I've made these tests and graphes for my thesis > talk, and now I want to share them with you.... > > What you are observing here is very likely the effect of Linux using the > > processor for a longer time and kicking RTAI out of the cache. It is a > > well known side effect of raising the sampling period. Just run LXRT > > with the same load and a 1ms period, and you should observe a raise in > > latency. You're right. With a sample period of 1 ms using LXRT's testsuite/user/latency I got under heavy load: *** min: 1447, max: 97994 average: 22077 <Hit [RETURN] to stop> *** > I tried to (quickly) port the programm to LXRT, but I've had no success (yet). > I'll measure again with my skin, sampling period decresed to 100 us, on > monday. (I have no access to the machine during the weekend) My skin with 100 us: nanosleep jitter: min = -595 ns, max = 46689 ns, avg = 2017 ns The jitter dropps from ~115 (1 ms period) us to ~50 us (100 us period). > > I have just run testsuite/latency/latency, using the RTAI native > > user-space skin, and observed a maximum jitter of 21 us on a Duron 950 > > MHz with the same load as yours. RTAI/fusion (RTAI native userspace skin): the umodified version (100 us period) gives me: min = -236 ns, max = 48612 ns, avg = 330 ns, overrun = 0 raising to 1 ms period it shows: min = 590 ns, max = 102407 ns, avg = 27201 ns, overrun = 0 Thanks Gilles, for reminding me again of the different sampling periods! tnx - Marc -- #!/bin/sh set - `type $0` 'tr "[a-zA-Z]" "[n-za-mN-ZA-M]"';while [ "$2" != "" ];do \ shift;done; echo 'frq -a -rc '`echo "$0"| $1 `'>$UBZR/.`rpub signature|'`\ echo $1|$1`'`;rpub "Jr ner fvtangher bs obet. Erfvfgnapr vf shgvyr!"'|$1|sh
