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IDProjectCategoryView StatusLast Update
0005581CentOS-6timepublic2014-08-29 13:54
Reportersubtopia Assigned To 
PrioritynormalSeverityminorReproducibilityalways
Status newResolutionopen 
Product Version6.2 
Summary0005581: Constant clock drift under Hyper-V Host
DescriptionI'm running 6.2 under a Hyper-V host.
I'm seeing a pretty much constant increase in time of approx 0.0625 secs a minute, or 90 seconds per day - i.e. the centos clock is running too fast.
I'm using version 3.2 of the MS linux integration components with time syncronization enabled.
As I understand it, the Centos 6 kernel should no longer require settings to be added to the bootloader for it to work in a virtualized environment.

cat /sys/devices/system/clocksource/clocksource0/current_clocksource shows hyperv_clocksource

Steps To ReproduceCreate a Hyper-V VM with 1 virtual CPU.
Install Centos 6.2 and MS linux IC 3.2 on the guest.
Reboot.

Now run inside the VM ntpdate -q 0.centos.pool.ntp.org
Wait a while, run it again. You'll see the clock running faster than it should

As soon as the machine starts up, the time appears to be correct.
However, if I run ntpdate -q 0.centos.pool.ntp.org every minute the difference gets greater every time I run it.

It is 100% reproduceable, and appears to be at a constant rate.
The clock on the host remains the correct time.
TagsNo tags attached.

Activities

subtopia

subtopia

2012-03-08 16:42

reporter   ~0014632

Kernel version is 2.6.32-220.4.2.el6.x86_64
mps_surcouf

mps_surcouf

2014-08-29 13:54

reporter   ~0020781

I see the same behaviour in Cent OS 6.5 and Cent OS 7 (integrated hyper-v drivers) on hyper-v host 2008 R2.
Clock gains similar to yours 10s of seconds per day and always fast.

I use NTP to mitigate this but sometimes the jitter is too much for it and it loses sync.

Also I note that saving and restoring (we do this for backup as no VSS for Linux on 2008R2) occasionally does not set the time on restore and the clock does not recover from this.

I am not sure how hyperv_clocksource works but presumable there is no actual communication of time of day and it is more of a tick provider.

ie it never compares the time of the host and guest.


Thanks

Mike

Issue History

Date Modified Username Field Change
2012-03-08 16:40 subtopia New Issue
2012-03-08 16:42 subtopia Note Added: 0014632
2014-08-29 13:54 mps_surcouf Note Added: 0020781