[ntp:questions] Regular spike_detect on syslog

Mike Cook michael.cook at sfr.fr
Sun Sep 16 16:42:59 UTC 2018

> Le 16 sept. 2018 à 16:34, Jan Ceuleers <jan.ceuleers at computer.org> a écrit :
> On 16/09/18 14:15, Sean Austin Critica wrote:
>> Can I directly observe these sources and see which ones are stable
>> (maybe by dumping them periodically, remotely from a machine with a
>> known stable clock)? The OS in this case is RedHat EL 7.

you might check out https://www.pantz.org/software/cpufreq/usingcpufreqonlinux.html

I don’t have Redhat but I expect similar commands are available for showing scaling info.
The webpage mentions a Redhead package cpuspeed.
You should be able to get speed change stats from that. Works for Debian with their cpufrequtils commands.

It would be useful to check that you do not have any processes other than ntpd running or scheduled by cron, that set the clock.
Also check the clock drift rate without ntpd running. Best to do this after cold boot in case previous frequency mods are active.

> "Directly observe": no. But you can look at the kernel log to see which
> clock source the OS has selected:
> # dmesg | grep clocksource
> [    0.000000] clocksource: refined-jiffies: mask: 0xffffffff
> max_cycles: 0xffffffff, max_idle_ns: 7645519600211568 ns
> [    0.000000] clocksource: hpet: mask: 0xffffffff max_cycles:
> 0xffffffff, max_idle_ns: 79635855245 ns
> [    0.053021] clocksource: jiffies: mask: 0xffffffff max_cycles:
> 0xffffffff, max_idle_ns: 7645041785100000 ns
> [    0.181027] clocksource: Switched to clocksource hpet
> [    0.198695] clocksource: acpi_pm: mask: 0xffffff max_cycles:
> 0xffffff, max_idle_ns: 2085701024 ns
> [    0.906180] clocksource: tsc: mask: 0xffffffffffffffff max_cycles:
> 0x2879c5f06f2, max_idle_ns: 440795220049 ns
> [    1.931401] clocksource: Switched to clocksource tsc
> You can then look in your CPU's manual to determine whether the selected
> clocksource is influenced by SpeedStep (or whatever dynamic CPU speed
> changes are called these days).
> HTH, Jan
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