Comment 0 for bug 1744988

We observe NTP time drift on two servers running hwe kernels in Xenial. A few weeks ago we wanted to switch from 4.4 to 4.10. When rebooting the servers to the 4.10 kernel we were seeing a big time offset within minutes after booting. Despite running ntpd, it would not keep up and the offset stayed and kept growing over t.

Rebooting back into the 4.4 at the time we immediatly noticed the time stayed normal. Over time I have tested about a dozen versions making me think something has been introduced in kernel 4.10 that makes the clock go out of sync.

So what do we observe?

After 1 min uptime:
     remote refid st t when poll reach delay offset jitter
==============================================================================
*ntp4.bit.nl .PPS. 1 u 5 16 7 0.497 100.084 81.382
+ntp1.bit.nl 193.0.0.229 2 u 8 16 7 0.603 93.241 70.643
+ntp2.bit.nl 193.67.79.202 2 u 8 16 7 0.582 93.218 70.674
+ntp3.bit.nl 193.79.237.14 2 u 9 16 7 0.781 90.488 70.574

A couple of minutes later (and also hours/days, the offset just keeps growing over time)

     remote refid st t when poll reach delay offset jitter
==============================================================================
*ntp4.bit.nl .PPS. 1 u 13 16 377 0.447 400.198 151.335
+ntp1.bit.nl 193.0.0.229 2 u 13 16 377 0.313 400.561 151.339
+ntp2.bit.nl 193.67.79.202 2 u 13 16 377 0.517 400.445 151.398
+ntp3.bit.nl 193.79.237.14 2 u 12 16 377 0.934 402.013 151.384

As mentioned I tested about a dozen of kernels and I thought I got it pinpointed to a specific release when the drifting got introduced, 4.10rc1. Below the test results of the kernels I have tested up till today:

Tested: 4.4.0-112-generic: not affected
Tested: 4.8.0-41-generic: not affected
Tested: 4.8.0-58-generic : not affected
Tested: 4.9.0 mainline: not affected
Tested: 4.9.66 mainline: not affected
Tested: 4.10-rc1 mainline: affected
Tested: 4.10 mainline: affected
Tested: 4.10.0-38-generic: affected
Tested: 4.10.0-40-generic: affected
Tested: 4.13.0-16-generic: affected
Tested: 4.13.0-31-generic: affected
Tested: 4.14.3 mainline: affected
Tested: 4.15-rc1 mainline: affected

When I was about to file this bugreport about an hour ago I noticed 4.15-rc9 was present and thought I gave it a go to make sure I really tested the latest version. And while running it over an hour now it stable.

Mostl likely the following from the changelog is related the issue we are having:

Len Brown (3):
      x86/tsc: Future-proof native_calibrate_tsc()
      x86/tsc: Fix erroneous TSC rate on Skylake Xeon
      x86/tsc: Print tsc_khz, when it differs from cpu_khz

Both servers that are having issues on our side our equipped with the following cpu:

Cpu Model (from /proc/cpuinfo)
vendor_id : GenuineIntel
cpu family : 6
model : 85
model name : Intel(R) Xeon(R) Gold 6136 CPU @ 3.00GHz

Standard information as requested:
1:
Description: Ubuntu 16.04.3 LTS
Release: 16.04

2:
root@bit-host6:~# apt-cache policy linux-image-generic-hwe-16.04
linux-image-generic-hwe-16.04:
  Installed: 4.13.0.31.51
  Candidate: 4.13.0.31.51

3: Stable time

4: A big time offset