Re: [gentoo-user] ntp-client slows down the boot process

[Rich Freeman]

On Fri, Jul 26, 2019 at 11:32 AM YUE Daian <sheepduke@×××××.com> wrote:
>
> I switched to a faster NTP server. It still takes some seconds but
> better than before.
>
> Maybe you are right. Having correct system time is more important than
> several seconds...

You're never going to make NTP fast unless you're using a VERY
low-latency server - like something on your own LAN.  That is just the
nature of the protocol - it has to do a round trip, and of course to
do anything it needs the interface up, DNS, and so on, and all of
these will be starting from cold caches.  If you have non-local DNS
and non-local NTP then that is multiple round-trips to the internet.

>
> By the way does "rc_parallel" really makes a difference?
> I tried it once before but did not really see much difference.

I haven't used OpenRC in ages, but I'm guessing that NTP is set as a
dependency somewhere in the chain.  It does make sense - lots of
services do not like abrupt time changes so generic dependencies will
probably assume that you want to set your clocks before starting
anything.

I'm not sure how ntpdate implements time changes.  I know that ntpd
will slew the clock gradually for small corrections, but it is a
daemon so it can easily implement something like that.  A one-shot
correction will probably be instant, and thus will be more of an
impact on other services.

You can probably adjust the dependencies to suit your tastes, but of
course you'll have to keep in mind that time changes for running
services might or might not be a problem.  If you're fairly confident
in your hardware clock accuracy (assuming you even have one) that
isn't a big deal.  If you're talking about some system that doesn't
keep time when powered off/etc then you probably don't want your
database server to spin up thinking it is 1980 or whatever its epoch
is.

I did a quick check of what is being done with systemd and ntpdate is
needed before the time-sync target, and that is needed before starting
cron or any timer units (obvious requirement), and it is also required
before spinning up libvirt guests, which also makes sense so that
those initialize with a clean clock, though if they update themselves
maybe that isn't a hard requirement.

-- 
Rich