When the tsc is not stable on the host, including cpufreq changes and deep C state, or even migration into faster tsc host. To stop deep C states in which the TSC can stop, add
"processor.max_cstate=1" as a host kernel boot option.
To disable cpufreq (only necessary on hosts which lack constant_tsc flag in "flags" field of /proc/cpuinfo), edit /etc/sysconfig/cpuspeed
MIN_SPEED and MAX_SPEED variables to the highest frequency available.