Re: [chrony-users] Chrony offset and stability adjustments? (fwd)

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

For a few 10s of dollars you can hook up a gps/pps to your hadware and have it
discipline the base system clock (not the VM clocks) to better than 10musec
(and sometimes better than 1musec). You just need an interrupt line (eg a
serial or parallel port, although those ae becoming really rare these days).
Networks always have the problem that there can be delays in the networks
(including your hardware's network card through things like ammalgamation).

But unless your VM get their time directly from the hardware, this might all
be for nought, since from what I understand, there are just so many ways a
VM's time can go awry.

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/

---------- Forwarded message ----------
Date: Mon, 7 Jan 2019 09:28:50
From: Denny Page <dennypage@xxxxxx>
Reply-To: chrony-users@xxxxxxxxxxxxxxxxxxxx
To: chrony-users@xxxxxxxxxxxxxxxxxxxx
Cc: "LeBlanc, Daniel James" <daniel.leblanc@xxxxxxxxxxxxx>
Subject: Re: [chrony-users] Chrony offset and stability adjustments?

I don’t believe a guarantee of < 1 ms from true time is achievable inside a VM. Too many things happen in a VM system even when the host is not over subscribed.

For a few hundred dollars you can buy a small hardware device that serves NTP (or even PTP) based on GPS. Very, very cost effective.

Denny


> On Jan 07, 2019, at 07:11, LeBlanc, Daniel James <daniel.leblanc@xxxxxxxxxxxxx> wrote:
>
> Hi Miroslav.
>
> The requirement that we are trying to meet is " Time accuracy must be within 1 ms of true time.", as described in Section 5.18 of https://www.nena.org/resource/resmgr/standards/NENA-STA-010.2_i3_Architectu.pdf.
>
> I am currently connected to the NRC Internet-accessible time servers from our lab environment.  I am so close to meeting the spec (~1.3ms reported root dispersion) that I thought I would reach out to the experts to see if there was some adjustment that I might try.  :-)
>
> I am running chrony within a virtual environment (VM) so have disabled rtcsync and enabled rtcfile within the .conf file.  I will look at reducing the maxclockerror and increasing the minsamples setting.  Any additional items to consider would be appreciated!
>
> Thanks.
>
> Daniel J. LeBlanc, P.Eng., MBA, DTME | Senior Network Architect | Bell Canada


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