| Re: [chrony-users] Possible to get sub-millisecond accuracy? |
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- Subject: Re: [chrony-users] Possible to get sub-millisecond accuracy?
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Thu, 15 Jun 2017 15:15:40 +0200
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On Thu, Jun 15, 2017 at 08:58:40AM -0400, Chris Perl wrote:
> On Thu, Jun 15, 2017 at 8:48 AM, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
> > It works even with <7.4 kernels if there is only one interface which
> > supports HW timestamping as SOF_TIMESTAMPING_OPT_CMSG is not required
> > in such case.
>
> Oh, exciting, thanks!
>
> Does that mean exactly one up interface that supports HWTSTAMP_FILTER_ALL?
>
> Meaning, would I be ok if the other interfaces on the machine
> supported things like HWTSTAMP_FILTER_PTP_V1_L4_SYNC,
> HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ, etc, but did not support
> HWTSTAMP_FILTER_ALL?
No, that won't work. The filter applies to received packets. If an
interface doesn't have HWTSTAMP_FILTER_ALL, it can still generate
transmit timestamps and chronyd won't know from which interface it
came.
Please note that the OPT_CMSG option is needed only for IPv4. If you
could use NTP over IPv6, that should work even with multiple
interfaces.
--
Miroslav Lichvar
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