Checking your linux hardware clock source

Current clock source:
# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
tsc

And about the available clock sources:
# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc hpet acpi_pm

Source: http://serverfault.com/questions/459901/hpet-missing-from-available-clocksources-on-centos