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Date: Tue, 23 Jun 2015 16:42:01 +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: Antoine Durand <wanipof@gmail.com>
Cc: Xenomai <xenomai@xenomai.org>

[restoring cc list]

On 2015-06-23 16:25, Antoine Durand wrote:
> I can "repair" the linux system time by forcing clock source from
> refined-jiffies to tsc
> 
> $ echo tsc >
> /sys/devices/system/clocksource/clocksource0/current_clocksource
> 
> Linux used refined-jiffies due to those messages at boot :
> 
> tsc: Fast TSC calibration using PIT
> tsc: Detected 2100.042 MHz processor
> PTP clock support registered
> Switched to clocksource refined-jiffies
> Switche to clocksource tsc
> rtc_cmos: setting system clock to 2015-06-23 17:28:56 UTC (1435080536)
> Clocksource tsc unstable (delta = 128069998 ns)
> Switched to clocksource refined-jiffies

jiffies - that is not good and explains the unstable timebase.

> 
> I don't know why.
> I've a modern core i7 CPU with constant_tsc flag (in /proc/cpuinfo)
> 
> 
> here are my HZ config:
> 
> CONFIG_NO_HZ_COMMON=y
> # CONFIG_HZ_PERIODIC is not set
> CONFIG_NO_HZ_IDLE=y
> CONFIG_NO_HZ=y

OK, CONFIG_NO_HZ, but that is set here as well. I was thinking of
NO_HZ_FULL when Lennart mentioned it. That's not tested and may cause
troubles.

> # CONFIG_RCU_FAST_NO_HZ is not set
> # CONFIG_HZ_100 is not set
> # CONFIG_HZ_250 is not set
> # CONFIG_HZ_300 is not set
> CONFIG_HZ_1000=y
> CONFIG_HZ=1000
> 

We don't have the full picture of your config yet: Do you use CPU
frequency scaling? Or some specific powersaving modes?

Jan

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