Added some information to ListenCoresBucketsRatio documentation page already in trunk.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1748951 13f79535-47bb-0310-9956-ffa450edef68

diff --git a/docs/manual/mod/mpm_common.xml b/docs/manual/mod/mpm_common.xml
index af03c93e8082181273de79881081223a193bf09e..dbc9b78a7d4a3ad578728432bb8620d71182fcf9 100644 (file)
--- a/docs/manual/mod/mpm_common.xml
+++ b/docs/manual/mod/mpm_common.xml
@@ -276,6 +276,13 @@ in *BSDs.</compatibility>
     then make each child handle a single bucket (with round-robin distribution
     of the buckets at children creation time).</p>
 
+    <note><title>Meaning of "online" CPU core</title>
+    <p>On Linux (and also BSD) a CPU core can be turned on/off if 
+    <a href="https://www.kernel.org/doc/Documentation/cpu-hotplug.txt">Hotplug</a> 
+    is configured, therefore <directive>ListenCoresBucketsRatio</directive> needs to
+    take this parameter into account while calculating the number of buckets to create.</p>
+    </note>
+
     <p><directive>ListenCoresBucketsRatio</directive> can improve the
     scalability when accepting new connections is/becomes the bottleneck.
     On systems with a large number of CPU cores, enabling this feature has
@@ -285,7 +292,10 @@ in *BSDs.</compatibility>
     <p>There must be at least twice the number of CPU cores than the
     configured <var>ratio</var> for this to be active. The recommended
     <var>ratio</var> is <code>8</code>, hence at least <code>16</code>
-    cores should be available at runtime when this value is used.</p>
+    cores should be available at runtime when this value is used.
+    The right <var>ratio</var> to obtain maximum performance needs to be calculated
+    for each target system, testing multiple values and observing the variations in your 
+    key performance metrics.</p>
 </usage>
 </directivesynopsis>