Yo Hal! On Wed, 01 Mar 2017 15:24:08 -0800 Hal Murray <[email protected]> wrote:
> RFC1589 describes an in-kernel PLL that synchronizes the system clock to an
> external PPS signal.
RFC1589 is what the kernel did in 1995. Mills had input to an update
to the in kernel PLL in 1999. I have no idea about any changes after
that.
A quick search of git log showed no changes there for a while.
> Some/many OSes/distros don't ship a kernel that supports the
> in-kernel PLL. In particular, it isn't available in Linux when
> compiled with NO_HZ. I think that is an implementation detail rather
> than anything fundamental. NO_HZ saves power on idle systems. It's
> important for battery life on laptops.
NO_HZ is gone in Linux 4.10. If is sort of replaced by CONFIG_NO_HZ_IDLE
CONFIG_NO_HZ=y is the default in all in tree defconfig's.
> I think it is likely that we would get results similar to the
> in-kernel PLL if we copied the code to user-land and called it as
> soon as the PPS data was available.
Would be an interesting check. The code is in kernel/time/time.c
> We should work on a NO_HZ version of ntpd.
ntpd works just fine with NO_HZ_IDLE. I'm not sure how it exactly
compares to the other 2 options; NO_HZ_FULL and HZ_PERIODIC. But I
agree it could be better at power awareness.
RGDS
GARY
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