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

starlight at binnacle.cx starlight at binnacle.cx
Mon Mar 31 01:05:31 UTC 2008


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.

>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.





     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'




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