Re: [patch 0/3] ptp: Provide support for auxiliary clocks for PTP_SYS_OFFSET_EXTENDED

[Thomas Gleixner]

On Thu, Jun 26 2025 at 16:53, Miroslav Lichvar wrote:
> On Thu, Jun 26, 2025 at 03:27:28PM +0200, Thomas Gleixner wrote:
>> This is obviously incomplete as the user space steering daemon needs to be
>> able to correlate timestamps from these auxiliary clocks with the
>> associated PTP device timestamp. The PTP_SYS_OFFSET_EXTENDED IOCTL command
>> already supports to select clock IDs for pre and post hardware timestamps,
>> so the first step for correlation is to extend that IOCTL to allow
>> selecting auxiliary clocks.
>
>> Miroslav: This branch should enable you to test the actual steering via a
>> 	  PTP device which has PTP_SYS_OFFSET_EXTENDED support in the driver.
>
> Nice! I ran few quick tests and it seems to be working great. The
> observed delay and stability with an AUX clock synchronized to a PHC
> seems to be the same as with CLOCK_REALTIME.

Thank you for taking the time!

> Are there any plans to enable software timestamping of packets by
> AUX clocks?

I'm not aware of any plans or efforts so far, but obviously that'd be
the next logical step.

> That would allow an NTP/PTP instance using SW timestamps
> to be fully isolated from the adjustments of the CLOCK_REALTIME clock,
> e.g. to run an independent NTP/PTP server in a container. This might
> be tricky as the skb would likely need to contain the MONOTONIC_RAW
> timestamp to be converted later when it gets to a socket, so some
> history of adjustments of each clock would need to be saved and
> reapplied to the raw timestamp.

Either that or you could go and implement some BPF magic to take a
timestamp with a particular clock ID based on the packet type. But what
do I know? That's something the network wizards needs to figure out.

Thanks,

        tglx