[ntp:questions] high precision tracking: trying to understand sudden jumps

Bill Unruh unruh at physics.ubc.ca
Mon Mar 31 04:36:09 UTC 2008


On Sun, 30 Mar 2008, starlight at binnacle.cx wrote:

> At 04:51 PM 3/30/2008 -0700, Bill Unruh wrote:
>> Are those on the same day?
>
> Yes, same day.  Uncorrelated to anything I can identify
> or each other.  Same story on all the boxes.  Running
> a hefty multi-system compile with heavy NFS and Samba
> traffic does not produce these events, though it disturbs
> the Windows boxes slightly when CPU goes to 100%.
>
>> Which "linux" and which "windows" are those graphs since you
>> have 2 linux and 2 windows clients.
>
> That's the dual-core AMD 2.4GHz Athlon Tyan mobo whitebox
> runing Centos 4.5 SMP kernel.  Similar results on the
> Dell Dimension 2400 2.4GHz Intel P4 running Centos 4.5
> mono-processor kernel.
>
> Windows is a dual-core 3.4GHz Pentium D Tyan mobo whitebox
> running 2003 R2 SP2 standard server.
>
>> As I said, seeing the
>> peerstats files would be helpful (offset and roundtrip)
>
> Might try them later, but I can't belive a high-quality
> SMC switch is causing multi-millisecond delays.  Just not
> possible.  Pings are all about 400 microseconds, consistent
> but slightly different on each system.  Round trip is
> 800 microseconds.  Attaching the output from a bulk 'ntpq -p'
> 'ntptrace' script I have below.  Note that's 'ntptrace'
> version 4.1 since the 4.2 script has useless offset info.

I have had weird latencies on some switches here. 
And since all your machines are experiencing this, that switch is the only
commonality (or the ntp server). Do you have the peerstats on the server as
well to make sure that there are not some weird delays there.



>
>> Also these graphs seem to have cut off the spikes. Are the
>> spikes actaully higher or is that an illusion?
>
> Higher.  Sometimes 1ms, sometimes 5-6ms.
>
>> (Note the spikes are hundreds of usec, not many msec)
>
> That would be the ~1ms example, check out the other one.
>

I am also really really really disturbed that you have so many servers. You
are trying to test out one specific server. The others are simply liable to
confuse everything. For example ntp could for some bizarre reason, suddenly
decide to use one of those other sites as the preferred server and give a
glitch.

And what are all those CDMA servers? Set your system up with one single
source, the one you want to test.


>
>
>
>
>     remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
>   Endrun CDMA
> LOCAL(0)        LOCAL(0)        10 l   18   64  377    0.000    0.000   0.015
> *HOPF_S(0)       .CDMA.           0 l    6   16  377    0.000    0.000   0.015
>   Centos 32
> *eachna          .CDMA.           1 u    3   16  377    0.683   -0.004   0.009
> -tock.usno.navy. .USNO.           1 u  452 1024  377   20.678    1.432   2.822
> +navobs1.wustl.e .GPS.            1 u  479 1024  377   50.136   -1.513   0.164
> +time.nist.gov   .ACTS.           1 u  471 1024  377   66.528   -1.708   0.156
> -tick.ucla.edu   .GPS.            1 u  432 1024  377   87.372    3.296   0.085
>   Ultra 10
> *172.29.87.3     .CDMA.           1 u   11   16  377    0.869   -0.016   0.042
> 172.29.87.15: stratum 2, offset -0.000007, synch distance 0.00783
> 172.29.87.3: stratum 1, offset -0.000018, synch distance 0.00038, refid 'CDMA'
>   Ultra 80
> *172.29.87.3     .CDMA.           1 u    4   16  377    0.942   -0.012   0.012
> 172.29.87.17: stratum 2, offset -0.000038, synch distance 0.00685
> 172.29.87.3: stratum 1, offset -0.000017, synch distance 0.00038, refid 'CDMA'
>   44p
> *172.29.87.3     .CDMA.           1 u   13   16  377    0.809   -0.001   0.016
> 172.29.87.13: stratum 2, offset -0.000014, synch distance 0.00627
> 172.29.87.3: stratum 1, offset -0.000018, synch distance 0.00038, refid 'CDMA'
>   Centos 64
> *172.29.87.3     .CDMA.           1 u   12   16  377    0.664    0.003   0.487
> 172.29.87.19: stratum 2, offset -0.000009, synch distance 0.00720
> 172.29.87.3: stratum 1, offset -0.000018, synch distance 0.00038, refid 'CDMA'
>   W2K3 64
> *172.29.87.3     .CDMA.           1 u    4   16  377    0.734    0.053   0.014
> 172.29.87.20: stratum 2, offset -0.000060, synch distance 0.00650
> 172.29.87.3: stratum 1, offset -0.000019, synch distance 0.00038, refid 'CDMA'
>   XP 32 laptop
> *172.29.87.3     .CDMA.           1 u    7   16  377    0.819    0.468   0.256
> 172.29.87.12: stratum 2, offset -0.000173, synch distance 0.00655
> 172.29.87.3: stratum 1, offset -0.000017, synch distance 0.00038, refid 'CDMA'
>

-- 
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh at physics.ubc.ca
Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/



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