[ntp:questions] Re: ntpd PLL and clock overshoot
Bart Van Assche
bart.vanassche at gmail.com
Sun Oct 15 15:27:37 UTC 2006
A few days ago I reported that I measured a larger overshoot with nptd
4.2.0a than with ntpd 4.1.0. By this time I have performed several test
with ntpd 4.2.2p3, and it seems to perform significantly better than
previous versions: overshoot is within spec and it is more accurate than
other versions I tried (all tests have been performed with a Linux
kernel, versions 2.4.20, 2.6.10 and 2.6.13).
Dave, can you tell me what is wrong with Linux with regard to precision
timekeeping ?
Other people asked where the Linux implementation of the adjtimex()
system call can be found. Its implementation resides in source file
kernel/time.c, functions sys_adjtimex() and do_adjtimex(). See e.g.
http://www.kernelhq.cc/browse.py?css=taichi
David L. Mills wrote:
> With all of the machines here, including FreeBSD, Solaris, HP-UX, SunOS,
> Tru64 and HP-UX, the loop response in steady state is as I reported
> earlier. The results with Linux are highly suspect, as at least in some
> cases the timer interrupt frequency has been changed significantly
> without compensation in the kernel parameters. I have recommended to
> avoid Linux in any case involving precision timekeeping.
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