hm, it looks like 'off to kernel patching' to nail this one -m
Anfang der weitergeleiteten E-Mail: > Von: "Gilles Chanteperdrix" <[email protected]> > Betreff: Re: [Xenomai] Question on rt_timer_tsc() vs rt_timer_read() semantics > Datum: 03. November 2012 10:37:20 MEZ > An: "Michael Haberler" <[email protected]> > Kopie: [email protected] > > > Michael Haberler wrote: >> I'm porting the LinuxCNC realtime support to Xenomai, and that has its own >> latency-test program. >> >> I observe: >> - the xenomai latency test is generally acceptable >> - with the LinuxCNC latency-test program I see occasional spikes up to >> maybe 80-100uS >> >> >> the only difference in the code I could discern is: >> >> the xenomai src/testsuite/latency/latency.c code uses rt_timer_tsc() to >> read the timestamp >> my port currently uses rt_timer_read() >> >> the question is: >> >> a) did I commit a blunder and should just change rt_timer_read() to use >> rt_timer_tsc() and all be fine, because that could be the explanation for >> the spike > > Using rt_timer_read() instead of rt_timer_tsc() is probably not the cause > for the spike. The difference between rt_timer_read() and rt_timer_tsc() is > that on most platforms, rt_timer_tsc() is implemented without a system > call, so the measured latencies is closer to reality (and smaller). > >> b) should I look elsewhere for the cause? > > Yes. Two things you can do: > - show us the code of your latency test so that we can have a look at it > for obvious mistakes > - enable the I-pipe tracer in the kernel configuration and trigger a trace > freeze (like latency -f option) when you hit the spike. > > http://www.xenomai.org/index.php/I-pipe:Tracer > > Also note that if LinuxCNC code runs in kernel-space, you should not be > using the native API, but the RTDM API. > > -- > Gilles. > ------------------------------------------------------------------------------ LogMeIn Central: Instant, anywhere, Remote PC access and management. Stay in control, update software, and manage PCs from one command center Diagnose problems and improve visibility into emerging IT issues Automate, monitor and manage. Do more in less time with Central http://p.sf.net/sfu/logmein12331_d2d _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
