Update Question 4.2.2:

- Rewrite from scratch by the aid of Release Notes

Reviewed by:	trhodes, danger, remko
Approved by:	gabor (mentor)

en_US.ISO8859-1/books/faq/book.sgml

@@ -2138,14 +2138,26 @@
         </question>
 
         <answer>
-          <para>Yes.  SMP was enabled by default in the
-            <emphasis>GENERIC</emphasis> kernel as of &os; 5.2.</para>
+	  <para>Symmetric multi-processor (SMP) systems are generally
+	    supported by &os;, although in some cases, BIOS or
+	    motherboard bugs may generate some problems.  Persuing
+	    the &a.smp; may yield some clues.</para>
 
-          <para>The intention was also to enable it by default for
-	    the &os; 5.3 release, but problems running the SMP kernel
-	    on certain UP machines led to the decision to disable it
-	    until those problems can be addressed.  This is a priority
-	    for &os; 5.4.</para>
+	  <para>&os; will take advantage of HyperThreading (HTT) support
+	    on Intel CPUs that support this feature.  A kernel with the
+	    <literal>options SMP</literal> feature enabled will
+	    automatically detect the additional logical processors.  The
+	    default &os; scheduler treats the logical processors the
+	    same as additional physical processors; in other words, no
+	    attempt is made to optimize scheduling decisions given the
+	    shared resources between logical processors within the same
+	    CPU.  Because this naive scheduling can result in suboptimal
+	    performance, under certain circumstances it may be useful to
+	    disable the logical processors with the
+	    <varname>machdep.hlt_logical_cpus</varname> sysctl variable.
+	    It is also possible to halt any CPU in the idle loop with
+	    the <varname>machdep.hlt_cpus</varname> sysctl variable.
+	    The &man.smp.4; manual page has more details.</para>
         </answer>
       </qandaentry>
         </qandaset>