3.3. TSC Timer Synchronization on Opteron CPUs

The current generation of AMD64 Opteron processors can be susceptible to a large gettimeofday skew. This skew occurs when both cpufreq and the Time Stamp Counter (TSC) are in use. Red Hat Enterprise Linux for Real Time provides a method to prevent this skew by forcing all processors to simultaneously change to the same frequency. As a result, the TSC on a single processor never increments at a different rate than the TSC on another processor.

Procedure 3.2. Enabling TSC Timer Synchronization

  1. Open the /etc/default/grub file in your preferred text editor and append the parameters clocksource=tsc powernow-k8.tscsync=1 to the GRUB_CMDLINE_LINUX variable. This forces the use of TSC and enables simultaneous core processor frequency transitions.
    GRUB_CMDLINE_LINUX="rd.md=0 rd.lvm=0 rd.dm=0 $([ -x /usr/sbin/rhcrashkernel-param ] && /usr/sbin/rhcrashkernel-param || :) rd.luks=0 vconsole.keymap=us rhgb quiet clocksource=tsc powernow-k8.tscsync=1"
  2. You will need to restart your system for the changes to take effect.
Related Manual Pages

For more information, or for further reading, the following man page is related to the information given in this section.

  • gettimeofday(2)