Losing some ticks... checking if CPU frequency changed.

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The error message from `dmesg` listed below:

Losing some ticks... checking if CPU frequency changed.
warning: many lost ticks.
Your time source seems to be instable or some driver is hogging interupts
rip __do_softirq+0x4d/0xd0
Falling back to HPET

Here's a related bug report at Redhat.com

https://bugzilla.redhat.com/show_bug.cgi?id=55223

Updating to recent kernel will fix it for you.

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Its due to poor ACPI implementation for CPU throttling.
Change the clock source by changing your kernel boot options to clock=pmtmr or clock=pit

Disable Dynamic overclocking @BIOS

title Red Hat Enterprise Linux AS (2.6.9-5.ELsmp)
        root (hd0,0)
        kernel /vmlinuz-2.6.9-5.ELsmp ro root=LABEL=/ rhgb quiet clock=pit
#       kernel /vmlinuz-2.6.9-5.ELsmp ro root=LABEL=/ rhgb quiet
        initrd /initrd-2.6.9-5.ELsmp.img