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16.10. Improving Accuracy

Previously, test results indicated that disabling the tickless kernel capability could significantly improve the stability of the system clock, and thus improve the PTP synchronization accuracy (at the cost of increased power consumption). The kernel tickless mode can be disabled by adding nohz=off to the kernel boot option parameters. However, recent improvements applied to kernel-3.10.0-197.fc21 have greatly improved the stability of the system clock and the difference in stability of the clock with and without nohz=off should be much smaller now for most users.
The ptp4l and phc2sys applications can be configured to use a new adaptive servo. The advantage over the PI servo is that it does not require configuration of the PI constants to perform well. To make use of this for ptp4l, add the following line to the /etc/ptp4l.conf file:
clock_servo linreg
After making changes to /etc/ptp4l.conf, restart the ptp4l service from the command line by issuing the following command as root:
~]# systemctl restart ptp4l
To make use of this for phc2sys, add the following line to the /etc/sysconfig/phc2sys file:
-E linreg
After making changes to /etc/sysconfig/phc2sys, restart the phc2sys service from the command line by issuing the following command as root:
~]# systemctl restart phc2sys