[Twisted-Python] accurate periodic call

Tristan Seligmann mithrandi at mithrandi.net
Tue Feb 21 22:20:16 EST 2012

On Tue, Feb 21, 2012 at 1:05 PM, Phil Mayers <p.mayers at imperial.ac.uk> wrote:
> I realise this is tricky to solve, but I'll note it's not impossible for
> really REALLY big clock skews to happen. For example: recently we had a
> server kernel panic and need a cold reboot. The machine booted and read
> it's time from the CMOS clock, which was way WAY out. A minute or two
> after the machine had booted, NTP slewed the clock back by months...

This is kind of a nitpick, but I think it's a fairly important one:
"slewing" the clock refers to a process where the clock frequency is
adjusted to make it run faster or slower in order to catch up or lose
a few seconds, without any discontinuities in the clock. This is a
relatively slow process, so "slewing" the clock by months would take
millennia; instead, beyond a certain threshold (I think a few
seconds?), ntp will always step the clock, not slew it, which is when
applications start running into difficulty as stepping introduces a
discontinuity in the clock.
mithrandi, i Ainil en-Balandor, a faer Ambar

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