[Twisted-Python] a question about monotonic clock

Christopher Armstrong radix at twistedmatrix.com
Sun Oct 28 12:01:30 EDT 2012

On Sun, Oct 28, 2012 at 4:45 PM, Tristan Seligmann
<mithrandi at mithrandi.net>wrote:

> On Sun, Oct 28, 2012 at 5:22 PM, Christopher Armstrong
> <radix at twistedmatrix.com> wrote:
> > I think that for *certain* uncommon types of applications, even the very
> > minor skewing of ntp can cause problems, but I wonder if gelin yan has
> I'm having trouble imagining such an application. In particular, if
> the application is sensitive to such minor fluctuations in the time
> source, I don't see how it could operate on commodity hardware at all;
> such fluctuations are present regardless of whether ntp is slewing the
> clock or not. You would need to use a separate hardware time source
> that is more reliable, at which point ntp is essentially out of the
> picture.

I'm not speaking from experience, admittedly. How big exactly are the steps
in NTP skewing?

I'm remembering VOIP applications (or anything else with low-latency
streaming or real-time gaming or something like that), where you can have
timed intervals of ~20ms, and if you miss one, you drop packets and lower
the quality of the audio stream. In a case like that, using a monotonic
time source seems like it would be a good decision. That's why Twisted
should provide an API for scheduling calls based on one, if possible (that
doesn't seem like a contentious point to me; just the general applicability
of such a scheduling mechanism).

Christopher Armstrong
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