[ntp:questions] Drift from serial activity, VIA system, LInux
david at ex.djwhome.demon.co.uk.invalid
Sun Jun 8 09:10:55 UTC 2008
Hal Murray wrote:
> The quirk is that the drift changes when I run the monitoring
> program. It changes more if I poll faster. It changed by
> 20 ppm when I was polling with a 10 ms delay and it's more
> than 80 ppm and still climbing when I reduced the delay to 1 ms.
My first guess would be a bug in the tickless clock in some recent
Linuxes. If possible, disable this and see if it improves things. If
it does take it up with the Linux kernel developers (I think this one
came from Red Hat), but let us know as well, as this is something that
was introduced without consulting the NTP community.
Note that tickless clock processing also led to some unofficial changes
in ntpd, in Linux, which again are the responsibility of the Linux
Note, to operate with 1ms delays in a non-tickless system, you need a
1000Hz clock and that is vulnerable to lost interrupts from slow device
I'm assuming that the UPS monitoring program runs in user space,
otherwise it could be causing lost interrupts, itself.
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