Re: [Xenomai] ToD drift on i7-3740QM

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Thu, Jan 29, 2015 at 01:59:36PM +0100, Roland Pastorino wrote:
> 2015-01-29 13:25 GMT+01:00 Gilles Chanteperdrix
> <gilles.chanteperdrix@xenomai.org>:
> > On Sun, Jan 25, 2015 at 12:15:39PM +0100, Roland Pastorino wrote:
> >> Good morning everyone,
> >>
> >> I would like to know if some of you could give me a hint on how to
> >> solve my ToD drift problem.
> >> This question is similar to this one ->
> >> http://comments.gmane.org/gmane.linux.real-time.xenomai.users/19719
> >>
> >> Problem:
> >> After installing Xenomai and after the first reboot, my ToD drift was
> >> around 500000 us/s.
> >> After the second reboot, my ToD drift is around 500 us/s which I
> >> presume is still too high.
> >> I checked the troubleshooting information on Xenomai website but it didn't help.
> >>
> >> Machine and configuration:
> >> - PC = Thinkpad w530
> >> - cpu = i7-3740QM
> >> - kernel configuration file is attached. I followed the Xenomai
> >> website for the configuration.
> >> - cobalt kernel of Xenomai 3
> >> - Linux kernel 3.16
> >> - ipipe-core-3.16-x86-1.patch
> >> - Ubuntu 14.10
> >
> > Actually, the kernel configuration is not attached. But probably the
> > only interesting item is whether CONFIG_CPU_FREQ is missing.
> >
> >
> > --
> >                                             Gilles.
> 
> I've attached the kernel configuration this time...
> 
> CONFIG_CPU_FREQ is like this:
> # CPU Frequency scaling
> #
> # CONFIG_CPU_FREQ is not set
> 
> This is the result of configuring the kernel via 'makemenuconfig'.
> Also I noticed that the 'clocktest' can give different results
> (without rebooting my machine).
> For example now my ToD drift is around 67 us/s which is better but
> different from the previously mentioned results.
> The best I got was 0.6 us/s.

Linux and Xenomai do not necessarily use the same clock source, and
when they use the same, do not necessarily use the same frequency,
especially when Linux has NTP running. So, unless you launch
clocktest to watch CLOCK_HOST_REALTIME, a difference is expected.
But 500us/s is abnormal, something is off. You need to look at the
frequencies used by Linux and Xenomai, and see which one is off.


-- 
					    Gilles.