Page Comparison

...

• Load the kernel module ptp_kvm, either automatically at boot or manually.
  This will create the a ptp device in /dev/ptp0 device, which is the PTP clock. To determine which device is the one created by ptp kvm, simply check that the file /sys/class/ptpt/ptp*/clock_name does indeed say "KVM virtual PTP". 
  In this example, our ptp_kvm device is ptp0.

• Synchronize the system clock with the PTP clock.

...