Re: [ntp:questions] Precision changed after upgrade from ntp 4.2.4p4 to 4.2.6p2
On 04/05/2014 20:29, Caecilius wrote: After upgrading ntp from 4.2.4p4 to 4.2.6p2 as part of a Linux upgrade from Debian Lenny to Squueze, I've noticed that the precision variable has changed from -20 to -22. So it appears that my clock has now got a better precision. But the hardware is unchanged, and I'm running the same kernel. I thought the precision was dependent on the granularity of the system clock, which I would have expected to be independent of the ntp version and any other userland code. Am I misunderstanding something perhaps? Here's the outputs of ntpq -c rv on both versions: .. and what does the current development version (4.2.7p441) show? -- Cheers, David Web: http://www.satsignal.eu ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Precision changed after upgrade from ntp 4.2.4p4 to 4.2.6p2
On Sun, May 04, 2014 at 08:29:26PM +0100, Caecilius wrote: After upgrading ntp from 4.2.4p4 to 4.2.6p2 as part of a Linux upgrade from Debian Lenny to Squueze, I've noticed that the precision variable has changed from -20 to -22. So it appears that my clock has now got a better precision. But the hardware is unchanged, and I'm running the same kernel. I thought the precision was dependent on the granularity of the system clock, which I would have expected to be independent of the ntp version and any other userland code. Am I misunderstanding something perhaps? The older ntpd is probably using gettimeofday() which has microsecond resolution (-20 in the log scale) and not the nanosecond clock_gettime(). -- Miroslav Lichvar ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Precision changed after upgrade from ntp 4.2.4p4 to 4.2.6p2
On Mon, 5 May 2014 09:13:03 GMT, Miroslav Lichvar
mlich...@redhat.com wrote:
On Sun, May 04, 2014 at 08:29:26PM +0100, Caecilius wrote:
After upgrading ntp from 4.2.4p4 to 4.2.6p2 as part of a Linux upgrade
from Debian Lenny to Squueze, I've noticed that the precision variable
has changed from -20 to -22. So it appears that my clock has now got a
better precision. But the hardware is unchanged, and I'm running the
same kernel.
The older ntpd is probably using gettimeofday() which has microsecond
resolution (-20 in the log scale) and not the nanosecond
clock_gettime().
Thanks. That's exactly what's happening.
strace snippets show this for 4.2.6p2:
send(3, 29May 5 11:15:28 ntpd[9487]: ..., 86, MSG_NOSIGNAL) = 86
umask(0)= 022
umask(022) = 0
getuid32() = 0
clock_gettime(CLOCK_REALTIME, {1399284928, 331375894}) = 0
rt_sigaction(SIGHUP, {0x8058680, [], 0}, {SIG_DFL, [], 0}, 8) = 0
And this for 4.2.4p4:
send(3, 29May 5 11:06:46 ntpd[1724]: n..., 86, MSG_NOSIGNAL) = 86
umask(0)= 022
umask(022) = 0
getuid32() = 0
gettimeofday({1399284406, 133635}, NULL) = 0
rt_sigaction(SIGHUP, {0x8053aa0, [], 0}, {SIG_DFL}, 8) = 0
It looks like this change means that ntp is better able to know the
precision of the underlying clock. I find that 4.2.4p4 always reports
-20 on a Linux system, both when it's running on real hardware and
also when it's running in a virtual machine on a windows host.
But 4.2.6p2 will report -22 for linux on real hardware, and -15 on a
vm under windows.
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[ntp:questions] Precision changed after upgrade from ntp 4.2.4p4 to 4.2.6p2
After upgrading ntp from 4.2.4p4 to 4.2.6p2 as part of a Linux upgrade from Debian Lenny to Squueze, I've noticed that the precision variable has changed from -20 to -22. So it appears that my clock has now got a better precision. But the hardware is unchanged, and I'm running the same kernel. I thought the precision was dependent on the granularity of the system clock, which I would have expected to be independent of the ntp version and any other userland code. Am I misunderstanding something perhaps? Here's the outputs of ntpq -c rv on both versions: ntpq -c rv for ntp 4.2.4p4: assID=0 status=06f4 leap_none, sync_ntp, 15 events, event_peer/strat_chg, version=ntpd 4.2.4p4@1.1520-o Sun Nov 22 17:34:54 UTC 2009 (1), processor=i686, system=Linux/2.6.32.61-nta-20405, leap=00, stratum=3, precision=-20, rootdelay=11.891, rootdispersion=82.127, peer=60194, refid=178.18.118.13, reftime=d700bca2.cf74a3b2 Tue, Apr 22 2014 11:02:10.810, poll=10, clock=d700c225.252de5e0 Tue, Apr 22 2014 11:25:41.145, state=4, offset=-0.307, frequency=-89.946, jitter=0.434, noise=0.266, stability=0.029, tai=0 ntpq -c rv for ntp 4.2.6p2 associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync, version=ntpd 4.2.6p2@1.2194-o Sun Oct 17 13:45:13 UTC 2010 (1), processor=i686, system=Linux/2.6.32.61-nta-20405, leap=00, stratum=3, precision=-22, rootdelay=31.619, rootdisp=60.232, refid=217.114.59.3, reftime=d705fe90.065494fe Sat, Apr 26 2014 10:44:48.024, clock=d7060569.8677132b Sat, Apr 26 2014 11:14:01.525, peer=6347, tc=10, mintc=3, offset=0.161, frequency=-89.952, sys_jitter=0.247, clk_jitter=0.196, clk_wander=0.017 ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
