[system-administrators-guide] Updates to: Improving Accuracy (PTP)

[stephenw]

commit 59d5790e52f90c22463f3af35ce23d6c2dd98b77
Author: Stephen Wadeley <swadeley at redhat.com>
Date:   Tue Dec 16 21:56:20 2014 +0100

    Updates to: Improving Accuracy (PTP)

 en-US/Configuring_PTP_Using_ptp4l.xml |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)
---
diff --git a/en-US/Configuring_PTP_Using_ptp4l.xml b/en-US/Configuring_PTP_Using_ptp4l.xml
index 75e812e..0f5174c 100644
--- a/en-US/Configuring_PTP_Using_ptp4l.xml
+++ b/en-US/Configuring_PTP_Using_ptp4l.xml
@@ -695,8 +695,20 @@ If required to use <systemitem class="daemon">ntpd</systemitem> as the <systemit
 <section id="sec-Improving_Accuracy">
   <title>Improving Accuracy</title>
   <para>
-    Test results indicate that disabling the tickless kernel capability can significantly improve the stability of the system clock, and thus improve the <systemitem class="protocol">PTP</systemitem> synchronization accuracy (at the cost of increased power consumption). The kernel tickless mode can be disabled by adding <option>nohz=off</option> to the kernel boot option parameters.
+    Previously, test results indicated that disabling the tickless kernel capability could significantly improve the stability of the system clock, and thus improve the <systemitem class="protocol">PTP</systemitem> synchronization accuracy (at the cost of increased power consumption). The kernel tickless mode can be disabled by adding <option>nohz=off</option> to the kernel boot option parameters. However, recent improvements applied to <filename>kernel-3.10.0-197.fc21</filename> have greatly improved the stability of the system clock and the difference in stability of the clock with and without <option>nohz=off</option> should be much smaller now for most users.
   </para>
+  <para>
+  The <application>ptp4l</application> and <application>phc2sys</application> 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 <application>ptp4l</application>, add the following line to the <filename>/etc/ptp4l.conf</filename> file:
+  <synopsis>clock_servo linreg</synopsis>
+  After making changes to <filename>/etc/ptp4l.conf</filename>, restart the <application>ptp4l</application> service from the command line by issuing the following command as <systemitem class="username">root</systemitem>:
+<screen>~]# <command>systemctl restart ptp4l</command></screen>
+</para>
+<para>
+To make use of this for <application>phc2sys</application>, add the following line to the <filename>/etc/sysconfig/phc2sys</filename> file:
+  <synopsis>-E linreg</synopsis>
+After making changes to <filename>/etc/sysconfig/phc2sys</filename>, restart the <application>phc2sys</application> service from the command line by issuing the following command as <systemitem class="username">root</systemitem>:
+<screen>~]# <command>systemctl restart phc2sys</command></screen>
+</para>
 </section>
 
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