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

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

On Tue, Feb 03, 2015 at 09:09:48AM +0100, Roland Pastorino wrote:
> 2015-01-30 12:15 GMT+01:00 Roland Pastorino <roland@rolandpastorino.com>:
> > 2015-01-29 14:04 GMT+01:00 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.
> >
> > I see the point.
> > If I run the 'clocktest' with CLOCK_HOST_REALTIME, I get this:
> >
> > == Tested clock: 8 (CLOCK_HOST_REALTIME)
> > CPU      ToD offset [us] ToD drift [us/s]      warps max delta [us]
> > --- -------------------- ---------------- ---------- --------------
> >   0         -339532135.1       122526.008          0            0.0
> >   1         -339532070.5       121839.520          0            0.0
> >   2         -339532420.1       122929.781          0            0.0
> >   3         -339531750.8       123088.126          0            0.0
> >
> > The drift is still way off.
> > CLOCK_REALTIME gives:
> >
> > == Tested clock: 0 (CLOCK_REALTIME)
> > CPU      ToD offset [us] ToD drift [us/s]      warps max delta [us]
> > --- -------------------- ---------------- ---------- --------------
> >   0         -302580987.5       330900.325          0            0.0
> >   1         -302580653.8       330346.234          0            0.0
> >   2         -302580710.2       329623.634          0            0.0
> >   3         -302580359.1       329730.306          0            0.0
> >
> > I verified that NTP is running.
> > $ sudo service ntp service
> > * NTP server is running
> >
> > As you mentioned the Linux and/or Xenomai frequencies is/are probably off.
> > I have to mention that my Linux clock (=date) can run faster or slower
> > than the wall-clock time.
> > Could you please tell me where I should start searching for a
> > solution? Linux kernel sources, ipipe patch?
> >
> > Many Thanks.
> >
> > Roland Pastorino
> 
> I give you more insight into the problem.
> I prepared a Linux kernel 3.14.17 with Xenomai 3 (instead of the 3.16
> I was using until now) in order to see if the problem disappeared.
> The kernel configuration is based on the one provided with Ubuntu
> 14.04 for kernel 3.13.
> With kernel 3.14.17 the problem remains. The only different is that
> the wifi on my PC now works.
> 
> Then I prepared a Linux kernel 3.16 without Xenomai in order to see if
> something was wrong with my compilation process.
> The kernel configuration is based on the one provided with Ubuntu
> 14.10 for kernel 3.16.
> This kernel works perfectly.
> 
> I welcome any comment/idea on how to proceed with the issue searching.

As I said, you need to look at the frequencies used by Linux and
Xenomai, and see which one is off.

-- 
					    Gilles.