| Re: [chrony-users] Best strategy for calculating average synchronization time. |
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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 |____ unruh@xxxxxxxxxxxxxx
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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