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- Subject: Re: [chrony-users] chronyc tracking question
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Tue, 25 Apr 2017 17:35:38 +0200
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On Tue, Apr 25, 2017 at 08:19:54AM -0700, Bill Unruh wrote:
> On Tue, 25 Apr 2017, Miroslav Lichvar wrote:
> > For example, here is a client with an Intel i210 card running two
> > chronyd instances using the same server. One is using HW timestamping
> > and controlling the clock, the other is using SW timestamping and just
> > monitoring the server with the noselect option.
>
> Running two instances of chrony means that one has to wait with its interrupt
> while the other finishes. That can give a large delay. I once tried that (not
> with one doing hardware timestamping however) and found a large delay (about
> 10us if I remember correctly) of the second waiting for the first.
The two instances are sending and receiving packets at different
times, which are timestamped by the kernel or the HW, so I think it
shouldn't matter. Currently it's necessary to use separate instances
for experiments like this, because the kernel doesn't allow SW
timestamping to be used together with HW timestamping. I'm working on
some patches that should remove this limitation.
--
Miroslav Lichvar
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