AW: Difference between Xenomai timer and Linux clock

[Prasanna Kannan <prasanna.kannan@ipg-automotive.com>]

> -----Ursprüngliche Nachricht-----
> Von: Chen, Hongzhan [mailto:hongzhan.chen@intel.com]
> Gesendet: Montag, 30. Mai 2022 02:56
> An: Prasanna Kannan <prasanna.kannan@ipg-automotive.com>;
> xenomai@xenomai.org
> Betreff: RE: Difference between Xenomai timer and Linux clock
>
>
>
> >-----Original Message-----
> >From: Xenomai <xenomai-bounces@xenomai.org> On Behalf Of Prasanna
> >Kannan via Xenomai
> >Sent: Friday, May 27, 2022 9:39 PM
> >To: xenomai@xenomai.org
> >Subject: Difference between Xenomai timer and Linux clock
> >
> >Hello Everybody,
> >
> >I am comparing the Xenomai Timer(rt_timer_read()) and clock_gettime()
> >with CLOCK_REALTIME and found that the two drift at roughly 100 us/s
> >Here is the snippet from my code:
> >
> >init():
> >clock_gettime(CLOCK_REALTIME, &ts_start); rtime_start =
> >rt_timer_read();
> >
> >runtime():
> >clk_xenotime = (rt_timer_read() - rtime_start) * 1e-9;
> >clock_gettime(CLOCK_REALTIME, &ts); clk_rttime = (ts.tv_sec -
> >ts_start.tv_sec) + (ts.tv_nsec -
> >ts_start.tv_nsec) * 1e-9;
> >delta = clk_rttime - clk_xenotime
> >
> >The observation is that the delta is around 100us/s ...
> >ClockGetTime:2.588435s, rt_timer_read:2.588167s, delta:0.000268s
> >ClockGetTime:3.588533s, rt_timer_read:3.588161s, delta:0.000372s
> >ClockGetTime:4.588671s, rt_timer_read:4.588196s, delta:0.000475s ...
> >
> >The Linux clock is not corrected via NTP/PTP, thus I am wondering why
> >they are drifting in this way.
> >
> >Some Information about my setup:
> >Xenomai/cobalt v3.1
> >Linux rtdonau 4.19.115-ipipe #54 SMP PREEMPT Wed Oct 13 12:16:56 CEST
> >2021
> >x86_64 GNU/Linux
> >Kernel parameters: intel_idle.max_cstate=0 vga=0x317 ip=dhcp
> >root=/dev/nfs
> >nfsroot=10.0.0.1:/opt/xyz/xeno_rt,tcp,nfsvers=3 BOOT_IMAGE=xeno10.2
> >I-pipe release #12 detected Cobalt core 3.1 detected
> >Compiler: gcc version 7.5.0 (GCC)
> >Build args: --prefix=/opt/xenomai-3.1 --enable-smp --enable-pshared
> >--enable-dlopen-libs
> >
> >The hardware used is an Intel SBC based on Core i7-4700EQ CPU @ 2.40GHz
>
> One of what we found is that there is delayed work which would refine
tsc
> clock after Xenomai init and that cause Clock difference which may
result in
> such drift.  The patchset "[Cobalt Xenoami3.1 PATCH 0/2] notify Xenomai
> udpated clockfreq."
> I sent in community at 5/27 try to fix what we found.  Could you send
your
> complete linux dmsg to check if our issues is the same?
>
Yes, I can confirm this as I see similar messages in my linux dmesg:
[    0.000000] tsc: Detected 2394.479 MHz processor
[    1.714630] tsc: Refined TSC clocksource calibration: 2394.455 MHz

[rtdonau-~] !) cat /sys/module/xenomai/parameters/clockfreq
2394479000
Attached my complete  dmesg.

> Regards
>
> Hongzhan Chen
> >
> >Thank you in Advance.
> >
> >Best Regards
> >Prasanna
> >
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