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Date: Tue, 23 Jun 2015 16:15:54 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: Re: [Xenomai] I-Pipe Tracer and linux ftrace
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To: Lennart Sorensen <lsorense@csclub.uwaterloo.ca>, Antoine Durand <wanipof@gmail.com>
Cc: xenomai@xenomai.org

On 2015-06-23 16:11, Lennart Sorensen wrote:
> On Tue, Jun 23, 2015 at 12:09:09PM +0200, Antoine Durand wrote:
>> I found a new problem that must be the root cause of the others (I hope)
>> the linux system time is wrong, one second last 31 real seconds !
>>
>> ftrace timing are wrong and may be nmi watchdog is fired because of that
>> wrong time too.
>>
>> however the time run normally in /proc/driver/rtc
>> (the CPU board get a Dallas DS12887 / Motorola MC146818 compatible RTC)
> 
> Normally the RTC is only used to get time at boot and save it when the
> system is off.  It usually has nothing at all to do with system time
> while the system is running.
> 
> So having the rtc correct but system time wrong is perfectly plausible
> if whatever is used for system time is broken.
> 
>> I use the CLOCK_MONOTONIC clock in xenomai periodic task and it works well.
>> I-Pipe tracer timing are correct too.
>>
>> in /proc/interrupts :
>> IRQ0 (timer) counter is not counting
>> LOC (local timer interrupts) is counting
>>
>> in /proc/xenomai/irq :
>> [timer/0] is counting (following LOC value)
>>
>> I'm trying to find why IRQ0 never happen.
> 
> Are you running NO_HZ config?
> 

Huh, that would be interesting...

Also check your Linux clocksource
(/sys/devices/system/clocksource/clocksource0/current_clocksource). It
should be TSC on sane systems. If not, check the kernel log for
clocksource switches and related reason reports.

Jan

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