[Pool] time reset

Ryan Tucker rtucker at gmail.com
Fri Mar 25 20:13:39 UTC 2011


On Fri, Mar 25, 2011 at 11:31:19AM -0700, Chuck Swiger wrote:
> Running ntpd is not easier than setting Xen's independent_wallclock = 0, or VMware's vmx option tools.syncTime = true.  As for best, well, I've yet to see data where that happens:
> 
> "6) I have yet to see an example where ntpd running in a DomU/guest kept
> better time than using independent_wallclock = 0, tools.syncTime = true, etc
> if the Dom0/host OS is sync'ed."

There is no independent_wallclock (or anything else that used to be in
/proc/sys/xen) for Linux domU running mainstream kernels with paravirt-ops.
It still exists on 2.6.18.8 with the legacy Xen patches, I believe, but
that was a long long time ago.

Interestingly, I have not noticed any NTP-related anomalies during periods
of high load.  CPU contention (identified by a nonzero steal%) is
relatively rare everywhere except Slicehost, but even there, it does not
seem to impact NTP's metrics.  IO contention is more common, but (as you
might expect) has no effect.

> ...or a long thread on comp.protocols.time.ntp (starting from Message-id:
> <568225d2-c7f0-4416-940b-9374da4d8003 at glegroupsg2000goo.googlegroups.com>) where a VM was seeing:

It looks like the original poster is running a pre-pvops Linux kernel within
Virtual PC running on a Windows system.  That will fail majestically at any
timing-critical task, like keeping time.

There are a number of different virtualization technologies in use, and
just because a few of them don't play well with ntpd doesn't mean that all
virtualization is immediately bad.  This was the case years ago, but not
any more.

Also, as requested, here's some ntpq -pcrv from a variety of VPSen:

# Linode (Newark, 512 MB)
# aka: http://www.pool.ntp.org/scores/97.107.134.213
rtucker at witte:~$ ssh framboise ntpq -pcrv
assID=0 status=06f4 leap_none, sync_ntp, 15 events, event_peer/strat_chg,
version="ntpd 4.2.4p4 at 1.1520-o Fri Dec  4 18:18:33 UTC 2009 (1)",
processor="i686", system="Linux/2.6.32.16-linode28", leap=00, stratum=2,
precision=-20, rootdelay=65.676, rootdispersion=23.570, peer=63002,
refid=99.27.25.65,
reftime=d1376b75.d71e4b43  Fri, Mar 25 2011 19:28:53.840, poll=10,
clock=d1376d04.4ec15567  Fri, Mar 25 2011 19:35:32.307, state=4,
offset=-0.142, frequency=4.648, jitter=1.172, noise=0.221,
stability=0.018, tai=0
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
-ntp3.tamu.edu   18.26.4.105      2 u  206 1024  377   53.796   -3.206
0.026
+tt155.ripe.Net  .GPS.            1 u  145 1024  377   89.838    0.727
0.098
 rhn-proxy01.dll 192.5.41.41      2 u  44d 1024    0   39.842   -0.325
0.000
-hennepin.ipv6.h 140.99.51.114    3 u  130 1024  377   49.925  -14.647
2.657
-ns1.anycast.cac 204.9.54.119     2 u  118 1024  377   19.193    0.867
0.004
+AC-NTP1.NET.CMU 128.10.254.7     2 u  200 1024  377   13.491    0.028
0.535
-morose.quex.org 66.187.233.4     2 u  243 1024  377   26.618   -4.730
0.136
*99-27-25-65.uvs .PPS.            1 u  400 1024  377   65.676   -1.059
0.088

# Slicehost (STL-A, 256 MB)
rtucker at witte:~$ ssh <redacted> ntpq -pcrv
assID=0 status=0644 leap_none, sync_ntp, 4 events, event_peer/strat_chg,
version="ntpd 4.2.4p8 at 1.1612-o Fri Apr  9 03:13:54 UTC 2010 (1)",
processor="x86_64", system="Linux/2.6.32.9-rscloud", leap=00, stratum=3,
precision=-20, rootdelay=105.261, rootdispersion=76.019, peer=59966,
refid=91.189.94.4,
reftime=d13765fd.3e4a247b  Fri, Mar 25 2011 19:05:33.243, poll=10,
clock=d1376d11.e0ed5c88  Fri, Mar 25 2011 19:35:45.878, state=4,
offset=-1.422, frequency=-41.286, jitter=0.065, noise=1.534,
stability=0.079, tai=0
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
*europium.canoni 193.79.237.14    2 u  788 1024  377   96.915   -1.422
1.271

# Rackspace Cloud (ORD, 512 MB)
rtucker at witte:~$ ssh <redacted> ntpq -pcrv
assID=0 status=0674 leap_none, sync_ntp, 7 events, event_peer/strat_chg,
version="ntpd 4.2.4p8 at 1.1612-o Fri Apr  9 03:13:54 UTC 2010 (1)",
processor="x86_64", system="Linux/2.6.35.4-rscloud", leap=00, stratum=3,
precision=-20, rootdelay=54.861, rootdispersion=72.824, peer=42528,
refid=69.36.227.90,
reftime=d137693f.e8b4a991  Fri, Mar 25 2011 19:19:27.909, poll=10,
clock=d1376d1e.c129a3aa  Fri, Mar 25 2011 19:35:58.754, state=4,
offset=-0.796, frequency=-24.309, jitter=4.690, noise=1.660,
stability=0.114, tai=0
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
+dosaku.ctipc.co 216.218.192.202  2 u 1023 1024  377   24.916    4.854
0.149
-vps1.cobryce.co 64.235.98.66     3 u  777 1024  377   58.442   -4.326
0.246
*name3.glorb.com 69.36.224.15     2 u  991 1024  377   50.604   -3.617
0.015
+lasvegas-nv-dat 67.18.187.111    3 u  738 1024  377   44.986   -1.490
11.508

# My desktop PC (HP with quad-core AMD Phenom II X4 830, not virtualized
# :-)
rtucker at witte:~$ ntpq -pcrv
assID=0 status=0684 leap_none, sync_ntp, 8 events, event_peer/strat_chg,
version="ntpd 4.2.4p8 at 1.1612-o Fri Apr  9 03:13:54 UTC 2010 (1)",
processor="x86_64", system="Linux/2.6.32-30-generic", leap=00,
stratum=3, precision=-20, rootdelay=33.886, rootdispersion=60.348,
peer=12205, refid=38.229.71.1,
reftime=d13767ce.04bfbe09  Fri, Mar 25 2011 15:13:18.018, poll=10,
clock=d1376d27.4c957687  Fri, Mar 25 2011 15:36:07.299, state=4,
offset=0.284, frequency=138.043, jitter=2.325, noise=2.388,
stability=0.126, tai=0
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
*clock.team-cymr 172.16.65.22     2 u  343 1024  377   32.467   -1.551
1.147
+mail.melancthon 138.39.23.13     2 u   33 1024  377   45.915    1.739
2.221
+206-217-140-200 184.106.219.19   3 u   85 1024  377   32.386    0.096
3.271

-- 
Ryan Tucker <rtucker at gmail.com>

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