[ntp:questions] Re: Frequent time reset messages

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Fri Jan 20 12:59:59 UTC 2006


Bob, the system clock may be broken for SMP, or your hardware may be
broken. Maybe also, your sofware config (speed-step technology, ACPI
throttling, power now, etc) is incompatible with NTP.

If you want to experiment, there's a set of patches by John Stultz (IBM I
think) for Linux 2.6 that implement a completely new system
clock. (experimental status right now)

Regards,
Ulrich


bob.robison at swri.org (Bob Robison) writes:

> I'm running a moderate number (around 50) dual-opterons that are
> diskless booting a Linux 2.6.12 smp kernel and trying to synch with a
> Symmetricon XLI-GPS stratum-1 NTP server on an isolated network.
> 
> The problem I have is that when I run "ntpq -c peers" on a number of
> these machines to check the status of the ntp synchronization, I see
> offsets ranging over almost 1000 msecs.  If I grep through the /var/log/
> messages file, I see that there are often messages around every 20
> minutes like this:
> 
> Dec  1 20:30:28 (none) ntpd[27203]: time reset 0.613771 s
> Dec  1 20:30:28 (none) ntpd[27203]: synchronisation lost
> Dec  1 20:50:45 (none) ntpd[27203]: time reset 0.931388 s
> Dec  1 20:50:45 (none) ntpd[27203]: synchronisation lost
> Dec  1 21:19:23 (none) ntpd[27203]: time reset 0.451491 s
> Dec  1 21:19:23 (none) ntpd[27203]: synchronisation lost
> Dec  1 21:36:24 (none) ntpd[27203]: time reset 0.391510 s
> Dec  1 21:36:24 (none) ntpd[27203]: synchronisation lost
> 
> This seems like large (and frequent) steps to be occuring.  I have a
> fairly simple ntp.conf file: 
> ---------------------------------
> restrict default ignore
> restrict 10.2.40.1 mask 255.255.255.255 nomodify notrap noquery
> restrict 127.0.0.1
> 
> server  10.2.40.1   iburst
> server  127.127.1.0     iburst # local clock
> fudge   127.127.1.0 stratum 5 # default was 10
> 
> driftfile /var/lib/ntp/drift
> ----------------------------------
> 
> These machines each have a Gigabit network connection to a high-end
> network switch.  I believe the NTP Server probably has only a 100MBit
> link, and he has all the traffic, but I don't think that is the
> problem.  
> 
> Probably the main issue is the CPU and I/O loading on these opteron
> machines.  They are each handling streaming data from a firewire card
> (IEEE-1394a) and the CPUs stay fairly busy handling that data -- though
> they are not pegged at 100% or anything.
> 
> Here is a typical ntpq output:
> ntpq> as
> ind assID status  conf reach auth condition  last_event cnt
> ===========================================================
>   1 48644  9634   yes   yes  none  sys.peer   reachable  3
>   2 48645  9034   yes   yes  none    reject   reachable  3
> ntpq> rv 48644
> status=9634 reach, conf, sel_sys.peer, 3 events, event_reach,
> srcadr=ntpserv, srcport=123, dstadr=10.1.1.1, dstport=123, leap=00,
> stratum=1, precision=-9, rootdelay=0.000, rootdispersion=5.554,
> refid=GPSM, reach=377, unreach=0, hmode=3, pmode=4, hpoll=7, ppoll=7,
> flash=00 ok, keyid=0, offset=360.879, delay=2.544, dispersion=3.803,
> jitter=6.636, reftime=c739efcd.cf993b0f  Thu, Dec  1 2005 21:55:25.810,
> org=c739efde.6ea22848  Thu, Dec  1 2005 21:55:42.432,
> rec=c739efde.1292f6e8  Thu, Dec  1 2005 21:55:42.072,
> xmt=c739efde.0c8ede54  Thu, Dec  1 2005 21:55:42.049,
> filtdelay=     2.54    4.42    2.50    2.98    2.55    2.61    2.44
> 2.68, 
> filtoffset=  360.88  354.24  412.02  412.20  464.11  -95.25
> -78.39  -56.90, 
> filtdisp=      1.96    3.90    5.82    7.77    9.70
> 11.62   12.61   13.57
> 
> If anyone has any suggestions about what might be happening, or how to
> keep these guys synched up more tightly, I would certainly appreciate
> it.  I've dug around through FAQs, Wiki's, Docs, etc... but not sure
> exactly why my time is bouncing around so much.
> 
> thanks in advance,
> bob
> -- 
> Bob Robison                        bob.robison at swri.org
> Staff Engineer                     210-522-3935
> Southwest Research Institute       San Antonio, TX
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