[ntp:questions] Re: program to test actual resolution of Linux?

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Tue Sep 9 14:35:05 UTC 2003

ryandrk at hotmail.com (Drk Ryan) writes:

> >>>But Windows provides a function, GetSystemTimeAsFileTime(), that
> >>>allows you to query the system time in 100 nanosecond intervals. 
> >>What you mean is that the function returns time with a theoretical
> >>resolution of 100ns. However it would appear likely that the actual
> >>times returned have a resolution of 10ms.  [rearranged slightly]
> >>Write a program that busy loop calls this function and saves the results
> >>over say 1000 calls.
> >I wrote a program that retrieved 10,000 unique values from the
> >GetSystemTimeAsFileTime() function, then analyzed the delta between
> >consecutive times. Out of 9,999 deltas, 9,974 of them were 10.144
> >milliseconds. 
> Does anyone have code available to do this for Linux?


call gettimeofday() twice and subtract. If you won't believe in the
method, describe what you are expecting as result.


P.S: If you are lazy:
ntpq> rl
status=06f4 leap_none, sync_ntp, 15 events, event_peer/strat_chg,
version="ntpd 4.1.1 at 1.786 Tue Feb  4 16:39:46 UTC 2003 (1)",
processor="i586", system="Linux2.4.19-4GB", leap=00, stratum=2,
precision=-18, rootdelay=44.226, rootdispersion=275.741, peer=23695,
reftime=c30861df.02caab8a  Tue, Sep  9 2003 16:27:43.010, poll=7,
clock=c308624c.95697f1f  Tue, Sep  9 2003 16:29:32.583, state=4,
offset=23.011, frequency=-15.395, jitter=15.000, stability=25.487

Precision means 2^-18 seconds...

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