Re: Best strategy for calculating average synchronization time.

These experiments are often run by people who have not throght through how a
something like chrony works. The problem you are looking at ver rarely happes
to a running system. Onely if you regularly turn off the computer is the
problem you are trying to solve a problem. Why in the world would Machinb B be
more than a second out from machine A. It is certainly NOT a problem for a
running system. And if you really want to  make it converge quickly, just tell
it to to jump the time if it is out by more than a second. In that case the
time it takes to converge is less than a second. On the other hand if you try
to do that for microseconds you will simply succeed in destableizing the
clock. 
A far far better test is to look to see how accurately a synchronized clock
tracks the true time. As Miroslav says, you need another accurate clock to do
so (eg a GPS clock) at which point you will find that chrony tracks to better
than a microsecond.


William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ [email protected]
Canada V6T 1Z1 ____|____ and Gravity ______|_    theory.physics.ubc.ca/

On Wed, 17 Jul 2024, Miroslav Lichvar wrote:

> [CAUTION: Non-UBC Email]
>
> On Wed, Jul 17, 2024 at 12:53:47PM +0000, Whelan, Andy wrote:
>> I want to try to try a bunch of experiments where we manually change the times on machine B and monitor how fast the system time on machine B synchronizes to, say within a second of Machine A. I want to calculate an average synchronization time.
>
> You would need an independent process measuring the error of the
> system clock. It could be a second chronyd instance running with the
> -x option using a much shorter polling interval.
>
> Please note that if you step the system clock of machine B behind
> chrony's back, you will disrupt its loop and it might take longer to
> recover than if you stepped the server's clock, or stepped the B's
> clock by using the chronyc settime and makestep commands.
>
> -- 
> Miroslav Lichvar
>
>
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