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Date:   Sat, 09 May 2020 11:49:27 +0200
From:   Thomas Gleixner <>
To:     Pali Rohár <>
Subject: Re: Missing CLOCK_BOOTTIME_RAW?


Pali Rohár <> writes:
> On Friday 08 May 2020 22:59:57 Thomas Gleixner wrote:
>> Pali Rohár <> writes:
>> Neither CLOCK_BOOTTIME nor CLOCK_MONOTONIC jump. They are frequency
>> corrected when NTP, PTP or PPS are in use. The frequency correction is
>> incremental an smothed. They really don't jump and they give you proper
>> time in nanoseconds which is as close to the real nanoseconds as it
>> gets.
> Hello! I should have been more precise about it. CLOCK_BOOTTIME and
> CLOCK_MONOTONIC do not jump but I understood that they are affected by
> adjtime(). So these clocks may tick faster or slower than real time. NTP
> daemon when see that CLOCK_REALTIME is incorrect, it may speed up or
> slow down its ticking. And this is affected also by CLOCK_BOOTTIME and

Sure, but what's the problem? The adjustemt is done to make the observed
time as correct as possible.

> You wrote that this clock is subject to drifts. What exactly may happen

  1) As the frequency of the raw clock is an estimate, resulting time
     is drifting apart vs. the correct frequency.

  2) Depending on the crystal/oszillator there can be temperatur drift as

Just for clarification. Even with NTP/PTP adjustment the resulting time
stamps are never going to be precise vs. an atomic clock, but good
enough for 99.9999% of the problems.

TBH, I have no idea what real world problem you are trying to solve.



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