Bounding the target platforms

[Gary E. Miller]

Yo Hal!

On Wed, 01 Mar 2017 15:24:08 -0800
Hal Murray <hmurray at megapathdsl.net> 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
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 455 bytes
Desc: OpenPGP digital signature
URL: <https://lists.ntpsec.org/pipermail/devel/attachments/20170301/f6bc9fbd/attachment.bin>