| Re: [chrony-users] Chrony offset and stability adjustments? (fwd) |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] Chrony offset and stability adjustments? (fwd)
- From: Bryan Christianson <bryan@xxxxxxxxxxxxx>
- Date: Wed, 9 Jan 2019 10:56:56 +1300
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Thanks for the explanations Miroslav. I guess I was just trying to illustrate that it is indeed possible to get sub-ms behaviour on VMs providing you have a good source of NTP.
> On 8/01/2019, at 10:31 PM, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
>
> In the estimate of the maximum error, it's important to include also
> half of the root delay, so in your examples it would be about 250
> microseconds.
OK - still less than 1ms as required by the OP.
Maybe this maximum error estimate could also be shown in 'chronyc tracking'?
>
> Raspberry PIs have ethernet on USB, which adds some latency, and IIRC
> the default interrupt coalescing is very large. You might want to try
> setting a smaller rx-usecs value with ethtool -C, which should reduce
> the root delay and give the clients a better estimate of the maximum
> error.
I had a quick look at this, but the nic in the RPi doesn't seem to support the coalesce options of ethtool with Debian Stretch.
As you say there may be better h/ware for the job, but the RPi/Uputronics combo is an inexpensive, and also well documented, way of getting very good timekeeping on a small LAN.
B
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Bryan Christianson
bryan@xxxxxxxxxxxxx
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