Fix “Clocksource tsc unstable” kernel message in a virtualized CentOS

If you use CentOS in a virtual environment it may be possible to get hundreds or messages like this from the kernel (using dmesg):

Clocksource tsc unstable (delta = -227342541 ns).  Enable clocksource failover by adding clocksource_failover kernel parameter.


First check which clocksources are available:

$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource

And which is being used at the moment:

$ cat /sys/devices/system/clocksource/clocksource0/current_clocksource

Most probably CentOS is using tsc and it also will be available acpi_pm.

To fix the issue edit /etc/grub.conf and add to the kernel configuration line clocksource_failover=acpi_pm:

kernel /vmlinuz-2.6.32-504.3.3.el6.x86_64 ro root=/dev/mapper/vg_centos-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=vg_centos/lv_swap  KEYBOARDTYPE=pc KEYTABLE=es rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=vg_centos/lv_root rd_NO_DM rhgb quiet clocksource_failover=acpi_pm

Then reboot and the problem should be gone.

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