Add CPU online/offline idea.

Submitted by:	jhb

en/projects/ideas/ideas.xml

@@ -15,7 +15,7 @@ Ideas//EN"
 <ideas>
   <cvs:keywords xmlns:cvs="http://www.FreeBSD.org/XML/CVS" version="1.0">
     <cvs:keyword name="freebsd">
-      $FreeBSD: www/en/projects/ideas/ideas.xml,v 1.124 2009/03/18 12:03:39 rwatson Exp $
+      $FreeBSD: www/en/projects/ideas/ideas.xml,v 1.125 2009/03/20 17:35:23 jkoshy Exp $
     </cvs:keyword>
   </cvs:keywords>
 
@@ -432,6 +432,35 @@ these buses to be a subclass of this new base class.</p>
       </desc>
     </idea>
 
+    <idea id="dynamiccpu" class="soc">
+      <title>CPU online/offline project</title>
+      <desc>
+	<p><strong>Technical contact</strong>: <a
+	  href="mailto:jhb@FreeBSD.org">John Baldwin</a></p>
+
+	<p>The project would need to extend the current CPU states of
+	  absent and present to include absent, offline, and online.  A
+	  set of event handlers (probably using EVENTHANDLER(9)) will
+	  need to be created to allow subsystems to be notified of CPU
+	  state changes.  At a minimum, the functionality of the
+	  current 'hlt_cpus_mask' should be reimplemented in both the
+	  4BSD and ULE schedulers using this mechanism.  Note that the
+	  ability to disable all but one thread within a core must
+	  still be supported easily.  (This is currently done on x86
+	  via the machdep.hyperthreading_allowed sysctl.)  Each
+	  subsystem that uses CPU_ABSENT() will need to be evaluated to
+	  see if it needs updating to handle online vs offline CPUs.
+	  Further improvements may include teaching UMA to free per-CPU
+	  buckets when a CPU is taken offline.</p>
+	<p><strong>Requirements</strong>:</p>
+	<ul>
+	  <li>Strong knowledge of C.</li>
+	  <li>Experience with multi-threaded programming.</li>
+	  <li>Experience with kernel programming.</li>
+	</ul>
+      </desc>
+    </idea>
+
       <idea id="docsysctl">
         <title>Document all sysctls</title>
         <desc>