[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
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.
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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