Brian Inglis wrote:
On 2014-09-04 04:58, Charles Elliott wrote:
When the platform clock is changed from the
performance counter (freq: 3.554 MHz) to the
HPET (freq: 14.318 MHz) the NTP protocol
precision declines from -22 to -20. This
occurs both in versions [email protected] May 09 10:14:35.18
and [email protected] Aug 28 12:01:29.42.
The NTPD_USE_INTERP_DANGEROUS=1 environment
variable is set. Here are the relevant messages from
the Event Log:
8/23/2014 3:34:59 PM Performance counter frequency 3.554 MHz
8/23/2014 3:34:59 PM proto: precision = 0.200 usec (-22)
8/23/2014 3:34:59 PM proto: fuzz beneath 0.100 usec
8/23/2014 3:52:37 PM Performance counter frequency 14.318 MHz
8/23/2014 3:52:38 PM proto: precision = 0.800 usec (-20)
→ → No "proto: fuzz beneath ... " message ← ←
Is this the way it should be, that the protocol precision
declines when the clock is more than 4 times faster?
Precision tells you how quickly ntpd can read the system timer,
not the resolution of the system timer.
See http://www.ntp.org/ntpfaq/NTP-s-sw-clocks-quality.htm
Especially for the Windows version of ntpd the reported precision can
depend on
- if it runs on Windows 8 or similar which provides the new precise time API
- whether timer tick interpolation is used, or not, on Windows versions
without precise time API
- which timer is used to implement QPC, or if TSC is used directly, if
interpolation is being used
Martin
--
Martin Burnicki
Meinberg Funkuhren
Bad Pyrmont
Germany
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