Re: [PATCH 5/5] [DO NOT MERGE] timekeeping: Apply extrapolated ntp_error to clock snapshots

[Rodolfo Giometti <giometti@enneenne.com>]

On 03/10/2026 00:47, David Woodhouse wrote:
> On Fri, 2026-10-02 at 12:26 +0200, Rodolfo Giometti wrote:
>>  
>>> So I think we do need it, and my inclination is to hold off on enabling
>>> CONFIG_NTP_PPS for tickless kernels until we do. But I'll defer to your
>>> preference. If you want to merge it sooner on the basis that with a
>>> 1PPS signal the system doesn't get to sleep for long *anyway*, I can do
>>> another test run with just patches 1-4.
>>>
>>
>> Yes, please do that run. This patch changes what PPS_FETCH returns to
>> userspace, so it has to wait for the chrony and ntpd people anyway; if
>> 1-4 alone are good enough at 1PPS I'd rather not tie the tickless
>> enablement to it.
> 
> https://david.woodhou.se/ntptest-r64/rodolfo-14-tickless-1hz/
> 
> Fairly much identical to the full series running tickless, which was
> https://david.woodhou.se/ntptest-r64/tickless-1hz/
> 
> And not really much worse than the tickful variant
> https://david.woodhou.se/ntptest-r64/tickful-1hz/
> 
> The ntp_error isn't measured because it's the clean series and most of
> the instrumentation is gone. I'll set the 5s pulse version running
> overnight.
> 
> The series is also tested on four virtual machines on the same host,
> tickful and tickless, patches vs. baseline. You can see the tickless
> baseline wobble when the actual frequency changes, while the other
> three remain stable. You can also see ntp_error on both baseline
> kernels spiking during the initial sync.
> https://david.woodhou.se/ntptest-virt/

Thanks, that's convincing: with 1-4 alone tickless at 1Hz looks the
same as with the full series, so I'm fine with the tickless enablement
not depending on this patch. :-)

Please put these numbers, and the 5s ones when you have them, in the commit
message of the patch dropping !NO_HZ_COMMON.

Ciao,

Rodolfo

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