Re: [chrony-users] makestep in Chrony

Hi Bill,

Sorry that I wasn't clear.

What I tried to do is to call clock_gettime() and rdtsc(p) as soon as chrony finishes synch so that I can get the best estimate when I try to derive time from (invariant) tsc.

Ideally, I have a C application that calls chrony's API (if there is one) similar to "chronyd -q" to block till it finishes or gets a callback.

Any suggestion?

On Thursday, May 10, 2018, 10:05:04 PM GMT+8, Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote:

I am not sure what you mean. chrony syncs constantly, and once it is running,
it, unless some disaster comes along, like you deciding to "test" it by
changing the clock out from under chrony, it will keep the clock within the
tightest bounds possible given the server/refclock it uses.
Just leave it be, and it will have your clock synced to the source as well as
possible. So, I am not sure what you have in mind. So, if you could tell us
what problem you are trying to fix, rather than asking what the best solution
to an unknown problem is, it would make answering much easier.

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 ______|_ www.theory.physics.ubc.ca/

On Thu, 10 May 2018, Hei Chan wrote:

> Thanks Miroslav and Bill!
>
> One last related question -- how can I be able to tell the sync/calibration is done
> after I manually ask chrony to synch/calibrate?
>
> I saw one of the posts 4 years ago suggesting that there is no way?
>
> Which command is better to force chrony to synchronize time right now -- chronyc burst
> or chronyc waitsync?
>
> WHICH COMMAND IS BETTER TO FORCE CHRONY TO SYNCHRONIZE TIME RIGHT NOW --...

>
>
> Or even better -- is there a way that I can call through a C API and get a callback or
> get blocked after it is done?
>
> Thanks!
>
> On Wednesday, May 9, 2018, 2:58:44 PM GMT+8, Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote:
>
>
>
>
> 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 ______|_ www.theory.physics.ubc.ca/
>
> On Wed, 9 May 2018, Miroslav Lichvar wrote:
>
> > On Sun, May 06, 2018 at 10:30:48AM +0000, Hei Chan wrote:
> >> Hi,
> >> I am reading this:https://chrony.tuxfamily.org/manual.html#makestep-command
> >> It mentions, "Normally chronyd will cause the system to gradually correct any time
> offset, by slowing down or speeding up the clock as required". Most of the Linux
> machines are using TSC as the source:$ cat
> /sys/devices/system/clocksource/clocksource0/current_clocksourcetsc
> >> Given a machine using TSC as the clock source and new Intel CPUs have invariant TSC,
> how can chrony slow down or speed up the clock? I am sure I misunderstand the doc.
> >
> > The clocksources don't change their frequency. It's the software
> > system clock maintained by the kernel, whose frequency is adjusted by
> > the adjtimex(2) system call.
>
> To expand, there is counter that counts the pulses in TSC, but those pulses
> need to be converted into seconds. That conversion factor can get changed by
> the adjtimex.
>
>