Re: [PATCH v4 0/4] Add ntp_error to clock snapshot, enable NTP_PPS on tickless kernel

[Rodolfo Giometti]

On Sat, 2026-08-29 at 21:56 +0100, David Woodhouse wrote:
> With this change, CONFIG_NTP_PPS works correctly on a tickless kernel;
> enable it. And change the non-CONFIG_NTP_PPS code path in pps_get_ts()
> to use ktime_get_snapshot_id() too, for the more accurate data.

Thanks for respinning. The idea is good, the !NO_HZ_COMMON dependency
has needed attention since 2011. Comments on 2/4 and 3/4 go in
separate mails. Here the general ones.

The series does not apply to mainline (v7.1-13176-g840ef6c78e6a). It
is written against some timekeeping rework that is not merged yet,
and there is no base-commit: and no word about which tree to use.
Please repost with "git format-patch --base=".

There is no changelog. Where are the v3 -> v4 notes? And why is this
now PATCH and no longer RFC?

3/4 does nothing at all without 1/4: it changes no timestamp value,
only the cost. So the series has to go through tip/timers as a unit,
not with the PPS bits going via Andrew separately.

1/4 itself is not mine to judge. It changes ::systime for every user of
ktime_get_snapshot_id() and get_device_system_crosststamp(), not only
PPS. Whether that is the right value for ptp4l and phc2sys is for
Richard and the PTP people to say. I raise it only because I want that
decision made explicitly, not inherited from a PPS series.

> Tested with a hack to make vmclock simulate a 1PPS signal, although there
> are now better options for that. But it's enough to show that even the
> tickless kernel converges to [...] the PPS signal and remains there
> (tested with a periodic PTP_SYS_OFFSET_EXTENDED to compare with the
> vmclock reference).

It is not enough. 4/4 takes the pulse from the same counter the
timekeeping reads, so there is no independent reference in the test at
all. Converging to +0ns against your own clock source proves very
little, and it says nothing about hardpps() driven by a real pulse.

You are asking me to undo something that has stood for fifteen years.
I am not going to ack that on this evidence. :) What I want to see
instead is in my reply to 2/4.

Rodolfo