[ntp:questions] Red Hat vote for chrony

Michael Deutschmann michael at talosis.ca
Fri Dec 12 11:58:53 UTC 2014


On Mon, 8 Dec 2014, Phil W Lee wrote:
> In theory, this wouldn't be expensive if done at the mass production
> stage, but clock stability isn't high enough on the design priorities
> for designers to put it into mass market machines.

It's been awhile since I've heard this whine on c.p.t.n.  Complaints
about cheap crystals in PC-compatibles used to be quite common, but they
seemed to have stopped for a while right after my intention to respond to
them crystallized (no pun intended).

I don't think a computer with a better "IRQ0" timer would be that useful.
NTP has survived quite well on what we have, and any serious clock nerd
uses external PPS anyway.  After all, a lot more people will pay extra for
a rubidium module in their GPS, than for one in their desktop....

There are better ways to upgrade a computer design for timekeeping.

For one thing, computers these days have dropped the RS-232 and parallel
connectors that used to be usable as a "geekport" to get PPS signals in
with lower and more consisent latency than USB.  Putting some sort of
geekport back in should be a higher priority than a better crystal.

The think *I* find most maddening about the PC design is that, ever since
the AT, there has been a circuit especially put there to track real time
-- the "CMOS clock".  But it has many flaws, so NTP and the OS ignore it
except at boot-up.

Change it to count time in 64-bit NTP format and allow subsecond reads,
writes and trimming and then it would become quite useful.  Especially
since it would free the OS to do anything it wants with the IRQ0 timer
without disrupting wallclock time.  "Tickless" kernels have been a thorn
in the side of clock nerds, but this would avert the conflict.

---- Michael Deutschmann <michael at talosis.ca>



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