On Thu, 2007-08-02 at 12:54 +0200, Johan Borkhuis wrote:
> Philippe Gerum wrote:
> > On Thu, 2007-08-02 at 11:47 +0200, Johan Borkhuis wrote:
> >
> >> I am experiencing an unexpected switch to secondary mode in a
> >> rt_timer_tsc2ns call from userspace.
> >>
> >> The following code give a switch:
> >> SRTIME timeStamp;
> >> timeStamp = rt_timer_tsc2ns(rt_timer_tsc());
> >> while((rt_timer_tsc2ns(rt_timer_tsc()) - timeStamp) < (usecs*1000)) {}
> >>
> >> while the following code does not:
> >> RTIME timeStamp;
> >> timeStamp = rt_timer_tsc();
> >> while((rt_timer_tsc() - timeStamp) < (usecs*1000)) {}
> >>
> >> (I know that the second example causes a longer timeout, but this was to
> >> show the testcase).
> >>
> >> When splitting up the 2nd line in the first example I see that the
> >> rt_timer_tsc() call does not cause a switch, but the rt_timer_tsc2ns
> >> does. What am I doing wrong here?
> >>
> >> I am using Xenomai-2.3.2.
> >>
> >>
> >
> > - Which CPU architecture, and which Adeos patch release are you using?
> >
> Processor: ppc 85xx, patch 1.5-03, Xenomai 2.3.2
>
> > - How do you notice the switches, SIGXCPU or /proc/xenomai/stat?
> >
> SIGXCPU
>
So it's unfortunately possible to experiment such switches on ppc hw for
now. It is likely happening when the ns value is copied back to a user
variable for which there is a PTE miss to handle in Linux kernel space
first. Check the mail archive about "pte", "cow" (copy-on-write) and
such things.
> Kind regards,
> Johan Borkhuis
>
--
Philippe.
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