[time-nuts] Re: PPS latency? User vs kernel mode

[Trent Piepho]

On Mon, Dec 13, 2021 at 6:56 AM Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
>
> In FreeBSD you get all that for free:
>
>         https://papers.freebsd.org/2002/phk-timecounters.files/timecounter.pdf
>

"It is painfully obvious that the interrupt latency is the dominant
noise factor in PPS timestamping in the second case."

This is exactly what I found when I did this 15 years after your
paper.  Though what I think is more interesting, is that despite using
15 years newer hardware, the resulting PPS precision ends up being
nearly the same for both timestamping methods.  Your final graphs are
very similar the one I have tried (succeeded?) at posting, other than
you using a time series I used a histogram.