Reorganisation of the source tree

Most of the other users of the fptools build system have migrated to
Cabal, and with the move to darcs we can now flatten the source tree
without losing history, so here goes.

The main change is that the ghc/ subdir is gone, and most of what it
contained is now at the top level.  The build system now makes no
pretense at being multi-project, it is just the GHC build system.

No doubt this will break many things, and there will be a period of
instability while we fix the dependencies.  A straightforward build
should work, but I haven't yet fixed binary/source distributions.
Changes to the Building Guide will follow, too.

1 files changed, 1440 insertions, 0 deletions

diff --git a/docs/users_guide/profiling.xml b/docs/users_guide/profiling.xml
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+<?xml version="1.0" encoding="iso-8859-1"?>
+<chapter id="profiling">
+  <title>Profiling</title>
+  <indexterm><primary>profiling</primary>
+  </indexterm>
+  <indexterm><primary>cost-centre profiling</primary></indexterm>
+
+  <para> Glasgow Haskell comes with a time and space profiling
+  system. Its purpose is to help you improve your understanding of
+  your program's execution behaviour, so you can improve it.</para>
+  
+  <para> Any comments, suggestions and/or improvements you have are
+  welcome.  Recommended &ldquo;profiling tricks&rdquo; would be
+  especially cool! </para>
+
+  <para>Profiling a program is a three-step process:</para>
+
+  <orderedlist>
+    <listitem>
+      <para> Re-compile your program for profiling with the
+      <literal>-prof</literal> option, and probably one of the
+      <literal>-auto</literal> or <literal>-auto-all</literal>
+      options.  These options are described in more detail in <xref
+      linkend="prof-compiler-options"/> </para>
+      <indexterm><primary><literal>-prof</literal></primary>
+      </indexterm>
+      <indexterm><primary><literal>-auto</literal></primary>
+      </indexterm>
+      <indexterm><primary><literal>-auto-all</literal></primary>
+      </indexterm>
+    </listitem>
+
+    <listitem>
+      <para> Run your program with one of the profiling options, eg.
+      <literal>+RTS -p -RTS</literal>.  This generates a file of
+      profiling information.</para>
+      <indexterm><primary><option>-p</option></primary><secondary>RTS
+      option</secondary></indexterm>
+    </listitem>
+      
+    <listitem>
+      <para> Examine the generated profiling information, using one of
+      GHC's profiling tools.  The tool to use will depend on the kind
+      of profiling information generated.</para>
+    </listitem>
+    
+  </orderedlist>
+  
+  <sect1 id="cost-centres">
+    <title>Cost centres and cost-centre stacks</title>
+    
+    <para>GHC's profiling system assigns <firstterm>costs</firstterm>
+    to <firstterm>cost centres</firstterm>.  A cost is simply the time
+    or space required to evaluate an expression.  Cost centres are
+    program annotations around expressions; all costs incurred by the
+    annotated expression are assigned to the enclosing cost centre.
+    Furthermore, GHC will remember the stack of enclosing cost centres
+    for any given expression at run-time and generate a call-graph of
+    cost attributions.</para>
+
+    <para>Let's take a look at an example:</para>
+
+    <programlisting>
+main = print (nfib 25)
+nfib n = if n &lt; 2 then 1 else nfib (n-1) + nfib (n-2)
+</programlisting>
+
+    <para>Compile and run this program as follows:</para>
+
+    <screen>
+$ ghc -prof -auto-all -o Main Main.hs
+$ ./Main +RTS -p
+121393
+$
+</screen>
+
+    <para>When a GHC-compiled program is run with the
+    <option>-p</option> RTS option, it generates a file called
+    <filename>&lt;prog&gt;.prof</filename>.  In this case, the file
+    will contain something like this:</para>
+
+<screen>
+          Fri May 12 14:06 2000 Time and Allocation Profiling Report  (Final)
+
+           Main +RTS -p -RTS
+
+        total time  =        0.14 secs   (7 ticks @ 20 ms)
+        total alloc =   8,741,204 bytes  (excludes profiling overheads)
+
+COST CENTRE          MODULE     %time %alloc
+
+nfib                 Main       100.0  100.0
+
+
+                                              individual     inherited
+COST CENTRE              MODULE      entries %time %alloc   %time %alloc
+
+MAIN                     MAIN             0    0.0   0.0    100.0 100.0
+ main                    Main             0    0.0   0.0      0.0   0.0
+ CAF                     PrelHandle       3    0.0   0.0      0.0   0.0
+ CAF                     PrelAddr         1    0.0   0.0      0.0   0.0
+ CAF                     Main             6    0.0   0.0    100.0 100.0
+  main                   Main             1    0.0   0.0    100.0 100.0
+   nfib                  Main        242785  100.0 100.0    100.0 100.0
+</screen>
+
+
+    <para>The first part of the file gives the program name and
+    options, and the total time and total memory allocation measured
+    during the run of the program (note that the total memory
+    allocation figure isn't the same as the amount of
+    <emphasis>live</emphasis> memory needed by the program at any one
+    time; the latter can be determined using heap profiling, which we
+    will describe shortly).</para>
+
+    <para>The second part of the file is a break-down by cost centre
+    of the most costly functions in the program.  In this case, there
+    was only one significant function in the program, namely
+    <function>nfib</function>, and it was responsible for 100&percnt;
+    of both the time and allocation costs of the program.</para>
+
+    <para>The third and final section of the file gives a profile
+    break-down by cost-centre stack.  This is roughly a call-graph
+    profile of the program.  In the example above, it is clear that
+    the costly call to <function>nfib</function> came from
+    <function>main</function>.</para>
+
+    <para>The time and allocation incurred by a given part of the
+    program is displayed in two ways: &ldquo;individual&rdquo;, which
+    are the costs incurred by the code covered by this cost centre
+    stack alone, and &ldquo;inherited&rdquo;, which includes the costs
+    incurred by all the children of this node.</para>
+
+    <para>The usefulness of cost-centre stacks is better demonstrated
+    by  modifying the example slightly:</para>
+
+    <programlisting>
+main = print (f 25 + g 25)
+f n  = nfib n
+g n  = nfib (n `div` 2)
+nfib n = if n &lt; 2 then 1 else nfib (n-1) + nfib (n-2)
+</programlisting>
+
+    <para>Compile and run this program as before, and take a look at
+    the new profiling results:</para>
+
+<screen>
+COST CENTRE              MODULE         scc  %time %alloc   %time %alloc
+
+MAIN                     MAIN             0    0.0   0.0    100.0 100.0
+ main                    Main             0    0.0   0.0      0.0   0.0
+ CAF                     PrelHandle       3    0.0   0.0      0.0   0.0
+ CAF                     PrelAddr         1    0.0   0.0      0.0   0.0
+ CAF                     Main             9    0.0   0.0    100.0 100.0
+  main                   Main             1    0.0   0.0    100.0 100.0
+   g                     Main             1    0.0   0.0      0.0   0.2
+    nfib                 Main           465    0.0   0.2      0.0   0.2
+   f                     Main             1    0.0   0.0    100.0  99.8
+    nfib                 Main        242785  100.0  99.8    100.0  99.8
+</screen>
+
+    <para>Now although we had two calls to <function>nfib</function>
+    in the program, it is immediately clear that it was the call from
+    <function>f</function> which took all the time.</para>
+
+    <para>The actual meaning of the various columns in the output is:</para>
+
+    <variablelist>
+      <varlistentry>
+	<term>entries</term>
+	<listitem>
+	  <para>The number of times this particular point in the call
+	  graph was entered.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>individual &percnt;time</term>
+	<listitem>
+	  <para>The percentage of the total run time of the program
+	  spent at this point in the call graph.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>individual &percnt;alloc</term>
+	<listitem>
+	  <para>The percentage of the total memory allocations
+	  (excluding profiling overheads) of the program made by this
+	  call.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>inherited &percnt;time</term>
+	<listitem>
+	  <para>The percentage of the total run time of the program
+	  spent below this point in the call graph.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>inherited &percnt;alloc</term>
+	<listitem>
+	  <para>The percentage of the total memory allocations
+	  (excluding profiling overheads) of the program made by this
+	  call and all of its sub-calls.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+
+    <para>In addition you can use the <option>-P</option> RTS option
+    <indexterm><primary><option>-P</option></primary></indexterm> to
+    get the following additional information:</para>
+
+    <variablelist>
+      <varlistentry>
+	<term><literal>ticks</literal></term>
+	<listitem>
+	  <para>The raw number of time &ldquo;ticks&rdquo; which were
+          attributed to this cost-centre; from this, we get the
+          <literal>&percnt;time</literal> figure mentioned
+          above.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><literal>bytes</literal></term>
+	<listitem>
+	  <para>Number of bytes allocated in the heap while in this
+          cost-centre; again, this is the raw number from which we get
+          the <literal>&percnt;alloc</literal> figure mentioned
+          above.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+
+    <para>What about recursive functions, and mutually recursive
+    groups of functions?  Where are the costs attributed?  Well,
+    although GHC does keep information about which groups of functions
+    called each other recursively, this information isn't displayed in
+    the basic time and allocation profile, instead the call-graph is
+    flattened into a tree.  The XML profiling tool (described in <xref
+    linkend="prof-xml-tool"/>) will be able to display real loops in
+    the call-graph.</para>
+
+    <sect2><title>Inserting cost centres by hand</title>
+
+      <para>Cost centres are just program annotations.  When you say
+      <option>-auto-all</option> to the compiler, it automatically
+      inserts a cost centre annotation around every top-level function
+      in your program, but you are entirely free to add the cost
+      centre annotations yourself.</para>
+
+      <para>The syntax of a cost centre annotation is</para>
+
+      <programlisting>
+     {-# SCC "name" #-} &lt;expression&gt;
+</programlisting>
+
+      <para>where <literal>"name"</literal> is an arbitrary string,
+      that will become the name of your cost centre as it appears
+      in the profiling output, and
+      <literal>&lt;expression&gt;</literal> is any Haskell
+      expression.  An <literal>SCC</literal> annotation extends as
+      far to the right as possible when parsing.</para>
+
+    </sect2>
+
+    <sect2 id="prof-rules">
+      <title>Rules for attributing costs</title>
+
+      <para>The cost of evaluating any expression in your program is
+      attributed to a cost-centre stack using the following rules:</para>
+
+      <itemizedlist>
+	<listitem>
+	  <para>If the expression is part of the
+	  <firstterm>one-off</firstterm> costs of evaluating the
+	  enclosing top-level definition, then costs are attributed to
+	  the stack of lexically enclosing <literal>SCC</literal>
+	  annotations on top of the special <literal>CAF</literal>
+	  cost-centre. </para>
+	</listitem>
+
+	<listitem>
+	  <para>Otherwise, costs are attributed to the stack of
+	  lexically-enclosing <literal>SCC</literal> annotations,
+	  appended to the cost-centre stack in effect at the
+	  <firstterm>call site</firstterm> of the current top-level
+	  definition<footnote> <para>The call-site is just the place
+	  in the source code which mentions the particular function or
+	  variable.</para></footnote>.  Notice that this is a recursive
+	  definition.</para>
+	</listitem>
+
+	<listitem>
+	  <para>Time spent in foreign code (see <xref linkend="ffi"/>)
+	  is always attributed to the cost centre in force at the
+	  Haskell call-site of the foreign function.</para>
+	</listitem>
+      </itemizedlist>
+
+      <para>What do we mean by one-off costs?  Well, Haskell is a lazy
+      language, and certain expressions are only ever evaluated once.
+      For example, if we write:</para>
+
+      <programlisting>
+x = nfib 25
+</programlisting>
+
+      <para>then <varname>x</varname> will only be evaluated once (if
+      at all), and subsequent demands for <varname>x</varname> will
+      immediately get to see the cached result.  The definition
+      <varname>x</varname> is called a CAF (Constant Applicative
+      Form), because it has no arguments.</para>
+
+      <para>For the purposes of profiling, we say that the expression
+      <literal>nfib 25</literal> belongs to the one-off costs of
+      evaluating <varname>x</varname>.</para>
+
+      <para>Since one-off costs aren't strictly speaking part of the
+      call-graph of the program, they are attributed to a special
+      top-level cost centre, <literal>CAF</literal>.  There may be one
+      <literal>CAF</literal> cost centre for each module (the
+      default), or one for each top-level definition with any one-off
+      costs (this behaviour can be selected by giving GHC the
+      <option>-caf-all</option> flag).</para>
+
+      <indexterm><primary><literal>-caf-all</literal></primary>
+      </indexterm>
+
+      <para>If you think you have a weird profile, or the call-graph
+      doesn't look like you expect it to, feel free to send it (and
+      your program) to us at
+      <email>glasgow-haskell-bugs@haskell.org</email>.</para>
+    </sect2>
+  </sect1>
+
+  <sect1 id="prof-compiler-options">
+    <title>Compiler options for profiling</title>
+
+    <indexterm><primary>profiling</primary><secondary>options</secondary></indexterm>
+    <indexterm><primary>options</primary><secondary>for profiling</secondary></indexterm>
+
+    <variablelist>
+      <varlistentry>
+	<term>
+          <option>-prof</option>:
+          <indexterm><primary><option>-prof</option></primary></indexterm>
+        </term>
+	<listitem>
+	  <para> To make use of the profiling system
+          <emphasis>all</emphasis> modules must be compiled and linked
+          with the <option>-prof</option> option. Any
+          <literal>SCC</literal> annotations you've put in your source
+          will spring to life.</para>
+
+	  <para> Without a <option>-prof</option> option, your
+          <literal>SCC</literal>s are ignored; so you can compile
+          <literal>SCC</literal>-laden code without changing
+          it.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+      
+    <para>There are a few other profiling-related compilation options.
+    Use them <emphasis>in addition to</emphasis>
+    <option>-prof</option>.  These do not have to be used consistently
+    for all modules in a program.</para>
+
+    <variablelist>
+      <varlistentry>
+	<term>
+          <option>-auto</option>:
+          <indexterm><primary><option>-auto</option></primary></indexterm>
+          <indexterm><primary>cost centres</primary><secondary>automatically inserting</secondary></indexterm>
+        </term>
+	<listitem>
+	  <para> GHC will automatically add
+          <function>&lowbar;scc&lowbar;</function> constructs for all
+          top-level, exported functions.</para>
+	</listitem>
+      </varlistentry>
+      
+      <varlistentry>
+	<term>
+          <option>-auto-all</option>:
+          <indexterm><primary><option>-auto-all</option></primary></indexterm>
+        </term>
+	<listitem>
+	  <para> <emphasis>All</emphasis> top-level functions,
+	  exported or not, will be automatically
+	  <function>&lowbar;scc&lowbar;</function>'d.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>
+          <option>-caf-all</option>:
+          <indexterm><primary><option>-caf-all</option></primary></indexterm>
+        </term>
+	<listitem>
+	  <para> The costs of all CAFs in a module are usually
+	  attributed to one &ldquo;big&rdquo; CAF cost-centre. With
+	  this option, all CAFs get their own cost-centre.  An
+	  &ldquo;if all else fails&rdquo; option&hellip;</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>
+          <option>-ignore-scc</option>:
+          <indexterm><primary><option>-ignore-scc</option></primary></indexterm>
+        </term>
+	<listitem>
+	  <para>Ignore any <function>&lowbar;scc&lowbar;</function>
+          constructs, so a module which already has
+          <function>&lowbar;scc&lowbar;</function>s can be compiled
+          for profiling with the annotations ignored.</para>
+	</listitem>
+      </varlistentry>
+
+    </variablelist>
+
+  </sect1>
+
+  <sect1 id="prof-time-options">
+    <title>Time and allocation profiling</title>
+
+    <para>To generate a time and allocation profile, give one of the
+    following RTS options to the compiled program when you run it (RTS
+    options should be enclosed between <literal>+RTS...-RTS</literal>
+    as usual):</para>
+
+    <variablelist>
+      <varlistentry>
+	<term>
+          <option>-p</option> or <option>-P</option>:
+          <indexterm><primary><option>-p</option></primary></indexterm>
+          <indexterm><primary><option>-P</option></primary></indexterm>
+          <indexterm><primary>time profile</primary></indexterm>
+        </term>
+	<listitem>
+	  <para>The <option>-p</option> option produces a standard
+          <emphasis>time profile</emphasis> report.  It is written
+          into the file
+          <filename><replaceable>program</replaceable>.prof</filename>.</para>
+
+	  <para>The <option>-P</option> option produces a more
+          detailed report containing the actual time and allocation
+          data as well.  (Not used much.)</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>
+          <option>-px</option>:
+          <indexterm><primary><option>-px</option></primary></indexterm>
+        </term>
+	<listitem>
+	  <para>The <option>-px</option> option generates profiling
+	  information in the XML format understood by our new
+	  profiling tool, see <xref linkend="prof-xml-tool"/>.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term>
+          <option>-xc</option>
+          <indexterm><primary><option>-xc</option></primary><secondary>RTS option</secondary></indexterm>
+        </term>
+	<listitem>
+	  <para>This option makes use of the extra information
+	  maintained by the cost-centre-stack profiler to provide
+	  useful information about the location of runtime errors.
+	  See <xref linkend="rts-options-debugging"/>.</para>
+	</listitem>
+      </varlistentry>
+
+    </variablelist>
+    
+  </sect1>
+
+  <sect1 id="prof-heap">
+    <title>Profiling memory usage</title>
+
+    <para>In addition to profiling the time and allocation behaviour
+    of your program, you can also generate a graph of its memory usage
+    over time.  This is useful for detecting the causes of
+    <firstterm>space leaks</firstterm>, when your program holds on to
+    more memory at run-time that it needs to.  Space leaks lead to
+    longer run-times due to heavy garbage collector activity, and may
+    even cause the program to run out of memory altogether.</para>
+
+    <para>To generate a heap profile from your program:</para>
+
+    <orderedlist>
+      <listitem>
+	<para>Compile the program for profiling (<xref
+	linkend="prof-compiler-options"/>).</para>
+      </listitem>
+      <listitem>
+	<para>Run it with one of the heap profiling options described
+	below (eg. <option>-hc</option> for a basic producer profile).
+	This generates the file
+	<filename><replaceable>prog</replaceable>.hp</filename>.</para>
+      </listitem>
+      <listitem>
+	<para>Run <command>hp2ps</command> to produce a Postscript
+	file,
+	<filename><replaceable>prog</replaceable>.ps</filename>.  The
+	<command>hp2ps</command> utility is described in detail in
+	<xref linkend="hp2ps"/>.</para> 
+      </listitem>
+      <listitem>
+	<para>Display the heap profile using a postscript viewer such
+	as <application>Ghostview</application>, or print it out on a
+	Postscript-capable printer.</para>
+      </listitem>
+    </orderedlist>
+
+    <sect2 id="rts-options-heap-prof">
+      <title>RTS options for heap profiling</title>
+
+      <para>There are several different kinds of heap profile that can
+      be generated.  All the different profile types yield a graph of
+      live heap against time, but they differ in how the live heap is
+      broken down into bands.  The following RTS options select which
+      break-down to use:</para>
+
+      <variablelist>
+	<varlistentry>
+	  <term>
+            <option>-hc</option>
+            <indexterm><primary><option>-hc</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Breaks down the graph by the cost-centre stack which
+	    produced the data.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hm</option>
+            <indexterm><primary><option>-hm</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Break down the live heap by the module containing
+	    the code which produced the data.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hd</option>
+            <indexterm><primary><option>-hd</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Breaks down the graph by <firstterm>closure
+	    description</firstterm>.  For actual data, the description
+	    is just the constructor name, for other closures it is a
+	    compiler-generated string identifying the closure.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hy</option>
+            <indexterm><primary><option>-hy</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Breaks down the graph by
+	    <firstterm>type</firstterm>.  For closures which have
+	    function type or unknown/polymorphic type, the string will
+	    represent an approximation to the actual type.</para>
+	  </listitem>
+	</varlistentry>
+	
+	<varlistentry>
+	  <term>
+            <option>-hr</option>
+            <indexterm><primary><option>-hr</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Break down the graph by <firstterm>retainer
+	    set</firstterm>.  Retainer profiling is described in more
+	    detail below (<xref linkend="retainer-prof"/>).</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hb</option>
+            <indexterm><primary><option>-hb</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Break down the graph by
+	    <firstterm>biography</firstterm>.  Biographical profiling
+	    is described in more detail below (<xref
+	    linkend="biography-prof"/>).</para>
+	  </listitem>
+	</varlistentry>
+      </variablelist>
+
+      <para>In addition, the profile can be restricted to heap data
+      which satisfies certain criteria - for example, you might want
+      to display a profile by type but only for data produced by a
+      certain module, or a profile by retainer for a certain type of
+      data.  Restrictions are specified as follows:</para>
+      
+      <variablelist>
+	<varlistentry>
+	  <term>
+            <option>-hc</option><replaceable>name</replaceable>,...
+            <indexterm><primary><option>-hc</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Restrict the profile to closures produced by
+	    cost-centre stacks with one of the specified cost centres
+	    at the top.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hC</option><replaceable>name</replaceable>,...
+            <indexterm><primary><option>-hC</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Restrict the profile to closures produced by
+	    cost-centre stacks with one of the specified cost centres
+	    anywhere in the stack.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hm</option><replaceable>module</replaceable>,...
+            <indexterm><primary><option>-hm</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Restrict the profile to closures produced by the
+	    specified modules.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hd</option><replaceable>desc</replaceable>,...
+            <indexterm><primary><option>-hd</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Restrict the profile to closures with the specified
+	    description strings.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hy</option><replaceable>type</replaceable>,...
+            <indexterm><primary><option>-hy</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Restrict the profile to closures with the specified
+	    types.</para>
+	  </listitem>
+	</varlistentry>
+	
+	<varlistentry>
+	  <term>
+            <option>-hr</option><replaceable>cc</replaceable>,...
+            <indexterm><primary><option>-hr</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Restrict the profile to closures with retainer sets
+	    containing cost-centre stacks with one of the specified
+	    cost centres at the top.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-hb</option><replaceable>bio</replaceable>,...
+            <indexterm><primary><option>-hb</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Restrict the profile to closures with one of the
+	    specified biographies, where
+	    <replaceable>bio</replaceable> is one of
+	    <literal>lag</literal>, <literal>drag</literal>,
+	    <literal>void</literal>, or <literal>use</literal>.</para>
+	  </listitem>
+	</varlistentry>
+      </variablelist>
+
+      <para>For example, the following options will generate a
+      retainer profile restricted to <literal>Branch</literal> and
+      <literal>Leaf</literal> constructors:</para>
+
+<screen>
+<replaceable>prog</replaceable> +RTS -hr -hdBranch,Leaf
+</screen>
+
+      <para>There can only be one "break-down" option
+      (eg. <option>-hr</option> in the example above), but there is no
+      limit on the number of further restrictions that may be applied.
+      All the options may be combined, with one exception: GHC doesn't
+      currently support mixing the <option>-hr</option> and
+      <option>-hb</option> options.</para>
+
+      <para>There are two more options which relate to heap
+      profiling:</para>
+
+      <variablelist>
+	<varlistentry>
+	  <term>
+            <option>-i<replaceable>secs</replaceable></option>:
+            <indexterm><primary><option>-i</option></primary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Set the profiling (sampling) interval to
+            <replaceable>secs</replaceable> seconds (the default is
+            0.1&nbsp;second).  Fractions are allowed: for example
+            <option>-i0.2</option> will get 5 samples per second.
+            This only affects heap profiling; time profiles are always
+            sampled on a 1/50 second frequency.</para>
+	  </listitem>
+	</varlistentry>
+
+	<varlistentry>
+	  <term>
+            <option>-xt</option>
+            <indexterm><primary><option>-xt</option></primary><secondary>RTS option</secondary></indexterm>
+          </term>
+	  <listitem>
+	    <para>Include the memory occupied by threads in a heap
+	    profile.  Each thread takes up a small area for its thread
+	    state in addition to the space allocated for its stack
+	    (stacks normally start small and then grow as
+	    necessary).</para>
+	    
+	    <para>This includes the main thread, so using
+	    <option>-xt</option> is a good way to see how much stack
+	    space the program is using.</para>
+
+	    <para>Memory occupied by threads and their stacks is
+	    labelled as &ldquo;TSO&rdquo; when displaying the profile
+	    by closure description or type description.</para>
+	  </listitem>
+	</varlistentry>
+      </variablelist>
+
+    </sect2>
+    
+    <sect2 id="retainer-prof">
+      <title>Retainer Profiling</title>
+
+      <para>Retainer profiling is designed to help answer questions
+      like <quote>why is this data being retained?</quote>.  We start
+      by defining what we mean by a retainer:</para>
+
+      <blockquote>
+	<para>A retainer is either the system stack, or an unevaluated
+	closure (thunk).</para>
+      </blockquote>
+
+      <para>In particular, constructors are <emphasis>not</emphasis>
+      retainers.</para>
+
+      <para>An object B retains object A if (i) B is a retainer object and
+     (ii) object A can be reached by recursively following pointers
+     starting from object B, but not meeting any other retainer
+     objects on the way. Each live object is retained by one or more
+     retainer objects, collectively called its retainer set, or its
+      <firstterm>retainer set</firstterm>, or its
+      <firstterm>retainers</firstterm>.</para>
+
+      <para>When retainer profiling is requested by giving the program
+      the <option>-hr</option> option, a graph is generated which is
+      broken down by retainer set.  A retainer set is displayed as a
+      set of cost-centre stacks; because this is usually too large to
+      fit on the profile graph, each retainer set is numbered and
+      shown abbreviated on the graph along with its number, and the
+      full list of retainer sets is dumped into the file
+      <filename><replaceable>prog</replaceable>.prof</filename>.</para>
+
+      <para>Retainer profiling requires multiple passes over the live
+      heap in order to discover the full retainer set for each
+      object, which can be quite slow.  So we set a limit on the
+      maximum size of a retainer set, where all retainer sets larger
+      than the maximum retainer set size are replaced by the special
+      set <literal>MANY</literal>.  The maximum set size defaults to 8
+      and can be altered with the <option>-R</option> RTS
+      option:</para>
+      
+      <variablelist>
+	<varlistentry>
+	  <term><option>-R</option><replaceable>size</replaceable></term>
+	  <listitem>
+	    <para>Restrict the number of elements in a retainer set to
+	    <replaceable>size</replaceable> (default 8).</para>
+	  </listitem>
+	</varlistentry>
+      </variablelist>
+
+      <sect3>
+	<title>Hints for using retainer profiling</title>
+
+	<para>The definition of retainers is designed to reflect a
+        common cause of space leaks: a large structure is retained by
+        an unevaluated computation, and will be released once the
+        computation is forced.  A good example is looking up a value in
+        a finite map, where unless the lookup is forced in a timely
+        manner the unevaluated lookup will cause the whole mapping to
+        be retained.  These kind of space leaks can often be
+        eliminated by forcing the relevant computations to be
+        performed eagerly, using <literal>seq</literal> or strictness
+        annotations on data constructor fields.</para>
+
+	<para>Often a particular data structure is being retained by a
+        chain of unevaluated closures, only the nearest of which will
+        be reported by retainer profiling - for example A retains B, B
+        retains C, and C retains a large structure.  There might be a
+        large number of Bs but only a single A, so A is really the one
+        we're interested in eliminating.  However, retainer profiling
+        will in this case report B as the retainer of the large
+        structure.  To move further up the chain of retainers, we can
+        ask for another retainer profile but this time restrict the
+        profile to B objects, so we get a profile of the retainers of
+        B:</para>
+
+<screen>
+<replaceable>prog</replaceable> +RTS -hr -hcB
+</screen>
+	
+	<para>This trick isn't foolproof, because there might be other
+        B closures in the heap which aren't the retainers we are
+        interested in, but we've found this to be a useful technique
+        in most cases.</para>
+      </sect3>
+    </sect2>
+
+    <sect2 id="biography-prof">
+      <title>Biographical Profiling</title>
+
+      <para>A typical heap object may be in one of the following four
+      states at each point in its lifetime:</para>
+
+      <itemizedlist>
+	<listitem>
+	  <para>The <firstterm>lag</firstterm> stage, which is the
+	  time between creation and the first use of the
+	  object,</para>
+	</listitem>
+	<listitem>
+	  <para>the <firstterm>use</firstterm> stage, which lasts from
+	  the first use until the last use of the object, and</para>
+	</listitem>
+	<listitem>
+	  <para>The <firstterm>drag</firstterm> stage, which lasts
+	  from the final use until the last reference to the object
+	  is dropped.</para>
+	</listitem>
+	<listitem>
+	  <para>An object which is never used is said to be in the
+	  <firstterm>void</firstterm> state for its whole
+	  lifetime.</para>
+	</listitem>
+      </itemizedlist>
+
+      <para>A biographical heap profile displays the portion of the
+      live heap in each of the four states listed above.  Usually the
+      most interesting states are the void and drag states: live heap
+      in these states is more likely to be wasted space than heap in
+      the lag or use states.</para>
+
+      <para>It is also possible to break down the heap in one or more
+      of these states by a different criteria, by restricting a
+      profile by biography.  For example, to show the portion of the
+      heap in the drag or void state by producer: </para>
+
+<screen>
+<replaceable>prog</replaceable> +RTS -hc -hbdrag,void
+</screen>
+
+      <para>Once you know the producer or the type of the heap in the
+      drag or void states, the next step is usually to find the
+      retainer(s):</para>
+
+<screen>
+<replaceable>prog</replaceable> +RTS -hr -hc<replaceable>cc</replaceable>...
+</screen>
+
+      <para>NOTE: this two stage process is required because GHC
+      cannot currently profile using both biographical and retainer
+      information simultaneously.</para>
+    </sect2>
+
+    <sect2 id="mem-residency">
+      <title>Actual memory residency</title>
+
+      <para>How does the heap residency reported by the heap profiler relate to
+	the actual memory residency of your program when you run it?  You might
+	see a large discrepancy between the residency reported by the heap
+	profiler, and the residency reported by tools on your system
+	(eg. <literal>ps</literal> or <literal>top</literal> on Unix, or the
+	Task Manager on Windows).  There are several reasons for this:</para>
+
+      <itemizedlist>
+	<listitem>
+	  <para>There is an overhead of profiling itself, which is subtracted
+	    from the residency figures by the profiler.  This overhead goes
+	    away when compiling without profiling support, of course.  The
+	    space overhead is currently 2 extra
+	    words per heap object, which probably results in
+	    about a 30% overhead.</para>
+	</listitem>
+
+	<listitem>
+	  <para>Garbage collection requires more memory than the actual
+	    residency.  The factor depends on the kind of garbage collection
+	    algorithm in use:  a major GC in the standard
+	    generation copying collector will usually require 3L bytes of
+	    memory, where L is the amount of live data.  This is because by
+	    default (see the <option>+RTS -F</option> option) we allow the old
+	    generation to grow to twice its size (2L) before collecting it, and
+	    we require additionally L bytes to copy the live data into.  When
+	    using compacting collection (see the <option>+RTS -c</option>
+	    option), this is reduced to 2L, and can further be reduced by
+	    tweaking the <option>-F</option> option.  Also add the size of the
+	    allocation area (currently a fixed 512Kb).</para>
+	</listitem>
+
+	<listitem>
+	  <para>The stack isn't counted in the heap profile by default.  See the
+    <option>+RTS -xt</option> option.</para>
+	</listitem>
+
+	<listitem>
+	  <para>The program text itself, the C stack, any non-heap data (eg. data
+	    allocated by foreign libraries, and data allocated by the RTS), and
+	    <literal>mmap()</literal>'d memory are not counted in the heap profile.</para>
+	</listitem>
+      </itemizedlist>
+    </sect2>
+
+  </sect1>
+
+  <sect1 id="prof-xml-tool">
+    <title>Graphical time/allocation profile</title>
+
+    <para>You can view the time and allocation profiling graph of your
+    program graphically, using <command>ghcprof</command>.  This is a
+    new tool with GHC 4.08, and will eventually be the de-facto
+    standard way of viewing GHC profiles<footnote><para>Actually this
+    isn't true any more, we are working on a new tool for
+    displaying heap profiles using Gtk+HS, so
+    <command>ghcprof</command> may go away at some point in the future.</para>
+      </footnote></para>
+
+    <para>To run <command>ghcprof</command>, you need
+    <productname>uDraw(Graph)</productname> installed, which can be
+    obtained from <ulink
+    url="http://www.informatik.uni-bremen.de/uDrawGraph/en/uDrawGraph/uDrawGraph.html"><citetitle>uDraw(Graph)</citetitle></ulink>.  Install one of
+    the binary
+    distributions, and set your
+    <envar>UDG_HOME</envar> environment variable to point to the
+    installation directory.</para>
+
+    <para><command>ghcprof</command> uses an XML-based profiling log
+    format, and you therefore need to run your program with a
+    different option: <option>-px</option>.  The file generated is
+    still called <filename>&lt;prog&gt;.prof</filename>.  To see the
+    profile, run <command>ghcprof</command> like this:</para>
+
+    <indexterm><primary><option>-px</option></primary></indexterm>
+
+<screen>
+$ ghcprof &lt;prog&gt;.prof
+</screen>
+
+    <para>which should pop up a window showing the call-graph of your
+    program in glorious detail.  More information on using
+    <command>ghcprof</command> can be found at <ulink
+    url="http://www.dcs.warwick.ac.uk/people/academic/Stephen.Jarvis/profiler/index.html"><citetitle>The
+    Cost-Centre Stack Profiling Tool for
+    GHC</citetitle></ulink>.</para>
+
+  </sect1>
+
+  <sect1 id="hp2ps">
+    <title><command>hp2ps</command>&ndash;&ndash;heap profile to PostScript</title>
+
+    <indexterm><primary><command>hp2ps</command></primary></indexterm>
+    <indexterm><primary>heap profiles</primary></indexterm>
+    <indexterm><primary>postscript, from heap profiles</primary></indexterm>
+    <indexterm><primary><option>-h&lt;break-down&gt;</option></primary></indexterm>
+    
+    <para>Usage:</para>
+    
+<screen>
+hp2ps [flags] [&lt;file&gt;[.hp]]
+</screen>
+
+    <para>The program
+    <command>hp2ps</command><indexterm><primary>hp2ps
+    program</primary></indexterm> converts a heap profile as produced
+    by the <option>-h&lt;break-down&gt;</option> runtime option into a
+    PostScript graph of the heap profile. By convention, the file to
+    be processed by <command>hp2ps</command> has a
+    <filename>.hp</filename> extension. The PostScript output is
+    written to <filename>&lt;file&gt;@.ps</filename>. If
+    <filename>&lt;file&gt;</filename> is omitted entirely, then the
+    program behaves as a filter.</para>
+
+    <para><command>hp2ps</command> is distributed in
+    <filename>ghc/utils/hp2ps</filename> in a GHC source
+    distribution. It was originally developed by Dave Wakeling as part
+    of the HBC/LML heap profiler.</para>
+
+    <para>The flags are:</para>
+
+    <variablelist>
+      
+      <varlistentry>
+	<term><option>-d</option></term>
+	<listitem>
+	  <para>In order to make graphs more readable,
+          <command>hp2ps</command> sorts the shaded bands for each
+          identifier. The default sort ordering is for the bands with
+          the largest area to be stacked on top of the smaller ones.
+          The <option>-d</option> option causes rougher bands (those
+          representing series of values with the largest standard
+          deviations) to be stacked on top of smoother ones.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-b</option></term>
+	<listitem>
+	  <para>Normally, <command>hp2ps</command> puts the title of
+          the graph in a small box at the top of the page. However, if
+          the JOB string is too long to fit in a small box (more than
+          35 characters), then <command>hp2ps</command> will choose to
+          use a big box instead.  The <option>-b</option> option
+          forces <command>hp2ps</command> to use a big box.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-e&lt;float&gt;[in&verbar;mm&verbar;pt]</option></term>
+	<listitem>
+	  <para>Generate encapsulated PostScript suitable for
+          inclusion in LaTeX documents.  Usually, the PostScript graph
+          is drawn in landscape mode in an area 9 inches wide by 6
+          inches high, and <command>hp2ps</command> arranges for this
+          area to be approximately centred on a sheet of a4 paper.
+          This format is convenient of studying the graph in detail,
+          but it is unsuitable for inclusion in LaTeX documents.  The
+          <option>-e</option> option causes the graph to be drawn in
+          portrait mode, with float specifying the width in inches,
+          millimetres or points (the default).  The resulting
+          PostScript file conforms to the Encapsulated PostScript
+          (EPS) convention, and it can be included in a LaTeX document
+          using Rokicki's dvi-to-PostScript converter
+          <command>dvips</command>.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-g</option></term>
+	<listitem>
+	  <para>Create output suitable for the <command>gs</command>
+          PostScript previewer (or similar). In this case the graph is
+          printed in portrait mode without scaling. The output is
+          unsuitable for a laser printer.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-l</option></term>
+	<listitem>
+	  <para>Normally a profile is limited to 20 bands with
+          additional identifiers being grouped into an
+          <literal>OTHER</literal> band. The <option>-l</option> flag
+          removes this 20 band and limit, producing as many bands as
+          necessary. No key is produced as it won't fit!. It is useful
+          for creation time profiles with many bands.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-m&lt;int&gt;</option></term>
+	<listitem>
+	  <para>Normally a profile is limited to 20 bands with
+          additional identifiers being grouped into an
+          <literal>OTHER</literal> band. The <option>-m</option> flag
+          specifies an alternative band limit (the maximum is
+          20).</para>
+
+	  <para><option>-m0</option> requests the band limit to be
+          removed. As many bands as necessary are produced. However no
+          key is produced as it won't fit! It is useful for displaying
+          creation time profiles with many bands.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-p</option></term>
+	<listitem>
+	  <para>Use previous parameters. By default, the PostScript
+          graph is automatically scaled both horizontally and
+          vertically so that it fills the page.  However, when
+          preparing a series of graphs for use in a presentation, it
+          is often useful to draw a new graph using the same scale,
+          shading and ordering as a previous one. The
+          <option>-p</option> flag causes the graph to be drawn using
+          the parameters determined by a previous run of
+          <command>hp2ps</command> on <filename>file</filename>. These
+          are extracted from <filename>file@.aux</filename>.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-s</option></term>
+	<listitem>
+	  <para>Use a small box for the title.</para>
+	</listitem>
+      </varlistentry>
+      
+      <varlistentry>
+	<term><option>-t&lt;float&gt;</option></term>
+	<listitem>
+	  <para>Normally trace elements which sum to a total of less
+          than 1&percnt; of the profile are removed from the
+          profile. The <option>-t</option> option allows this
+          percentage to be modified (maximum 5&percnt;).</para>
+
+	  <para><option>-t0</option> requests no trace elements to be
+          removed from the profile, ensuring that all the data will be
+          displayed.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><option>-c</option></term>
+	<listitem>
+	  <para>Generate colour output.</para>
+	</listitem>
+      </varlistentry>
+      
+      <varlistentry>
+	<term><option>-y</option></term>
+	<listitem>
+	  <para>Ignore marks.</para>
+	</listitem>
+      </varlistentry>
+      
+      <varlistentry>
+	<term><option>-?</option></term>
+	<listitem>
+	  <para>Print out usage information.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+
+
+    <sect2 id="manipulating-hp">
+      <title>Manipulating the hp file</title>
+
+<para>(Notes kindly offered by Jan-Willhem Maessen.)</para>
+
+<para>
+The <filename>FOO.hp</filename> file produced when you ask for the
+heap profile of a program <filename>FOO</filename> is a text file with a particularly
+simple structure. Here's a representative example, with much of the
+actual data omitted:
+<screen>
+JOB "FOO -hC"
+DATE "Thu Dec 26 18:17 2002"
+SAMPLE_UNIT "seconds"
+VALUE_UNIT "bytes"
+BEGIN_SAMPLE 0.00
+END_SAMPLE 0.00
+BEGIN_SAMPLE 15.07
+  ... sample data ...
+END_SAMPLE 15.07
+BEGIN_SAMPLE 30.23
+  ... sample data ...
+END_SAMPLE 30.23
+... etc.
+BEGIN_SAMPLE 11695.47
+END_SAMPLE 11695.47
+</screen>
+The first four lines (<literal>JOB</literal>, <literal>DATE</literal>, <literal>SAMPLE_UNIT</literal>, <literal>VALUE_UNIT</literal>) form a
+header.  Each block of lines starting with <literal>BEGIN_SAMPLE</literal> and ending
+with <literal>END_SAMPLE</literal> forms a single sample (you can think of this as a
+vertical slice of your heap profile).  The hp2ps utility should accept
+any input with a properly-formatted header followed by a series of
+*complete* samples.
+</para>
+</sect2>
+
+    <sect2>
+      <title>Zooming in on regions of your profile</title>
+
+<para>
+You can look at particular regions of your profile simply by loading a
+copy of the <filename>.hp</filename> file into a text editor and deleting the unwanted
+samples.  The resulting <filename>.hp</filename> file can be run through <command>hp2ps</command> and viewed
+or printed.
+</para>
+</sect2>
+
+    <sect2>
+      <title>Viewing the heap profile of a running program</title>
+
+<para>
+The <filename>.hp</filename> file is generated incrementally as your
+program runs.  In principle, running <command>hp2ps</command> on the incomplete file
+should produce a snapshot of your program's heap usage.  However, the
+last sample in the file may be incomplete, causing <command>hp2ps</command> to fail.  If
+you are using a machine with UNIX utilities installed, it's not too
+hard to work around this problem (though the resulting command line
+looks rather Byzantine):
+<screen>
+  head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+    | hp2ps > FOO.ps
+</screen>
+
+The command <command>fgrep -n END_SAMPLE FOO.hp</command> finds the
+end of every complete sample in <filename>FOO.hp</filename>, and labels each sample with
+its ending line number.  We then select the line number of the last
+complete sample using <command>tail</command> and <command>cut</command>.  This is used as a
+parameter to <command>head</command>; the result is as if we deleted the final
+incomplete sample from <filename>FOO.hp</filename>.  This results in a properly-formatted
+.hp file which we feed directly to <command>hp2ps</command>.
+</para>
+</sect2>
+    <sect2>
+      <title>Viewing a heap profile in real time</title>
+
+<para>
+The <command>gv</command> and <command>ghostview</command> programs
+have a "watch file" option can be used to view an up-to-date heap
+profile of your program as it runs.  Simply generate an incremental
+heap profile as described in the previous section.  Run <command>gv</command> on your
+profile:
+<screen>
+  gv -watch -seascape FOO.ps 
+</screen>
+If you forget the <literal>-watch</literal> flag you can still select
+"Watch file" from the "State" menu.  Now each time you generate a new
+profile <filename>FOO.ps</filename> the view will update automatically.
+</para>
+
+<para>
+This can all be encapsulated in a little script:
+<screen>
+  #!/bin/sh
+  head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+    | hp2ps > FOO.ps
+  gv -watch -seascape FOO.ps &amp;
+  while [ 1 ] ; do
+    sleep 10 # We generate a new profile every 10 seconds.
+    head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+      | hp2ps > FOO.ps
+  done
+</screen>
+Occasionally <command>gv</command> will choke as it tries to read an incomplete copy of
+<filename>FOO.ps</filename> (because <command>hp2ps</command> is still running as an update
+occurs).  A slightly more complicated script works around this
+problem, by using the fact that sending a SIGHUP to gv will cause it
+to re-read its input file:
+<screen>
+  #!/bin/sh
+  head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+    | hp2ps > FOO.ps
+  gv FOO.ps &amp;
+  gvpsnum=$!
+  while [ 1 ] ; do
+    sleep 10
+    head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+      | hp2ps > FOO.ps
+    kill -HUP $gvpsnum
+  done    
+</screen>
+</para>
+</sect2>
+
+
+  </sect1>
+
+  <sect1 id="ticky-ticky">
+    <title>Using &ldquo;ticky-ticky&rdquo; profiling (for implementors)</title>
+    <indexterm><primary>ticky-ticky profiling</primary></indexterm>
+
+    <para>(ToDo: document properly.)</para>
+
+    <para>It is possible to compile Glasgow Haskell programs so that
+    they will count lots and lots of interesting things, e.g., number
+    of updates, number of data constructors entered, etc., etc.  We
+    call this &ldquo;ticky-ticky&rdquo;
+    profiling,<indexterm><primary>ticky-ticky
+    profiling</primary></indexterm> <indexterm><primary>profiling,
+    ticky-ticky</primary></indexterm> because that's the sound a Sun4
+    makes when it is running up all those counters
+    (<emphasis>slowly</emphasis>).</para>
+
+    <para>Ticky-ticky profiling is mainly intended for implementors;
+    it is quite separate from the main &ldquo;cost-centre&rdquo;
+    profiling system, intended for all users everywhere.</para>
+
+    <para>To be able to use ticky-ticky profiling, you will need to
+    have built appropriate libraries and things when you made the
+    system.  See &ldquo;Customising what libraries to build,&rdquo; in
+    the installation guide.</para>
+
+    <para>To get your compiled program to spit out the ticky-ticky
+    numbers, use a <option>-r</option> RTS
+    option<indexterm><primary>-r RTS option</primary></indexterm>.
+    See <xref linkend="runtime-control"/>.</para>
+
+    <para>Compiling your program with the <option>-ticky</option>
+    switch yields an executable that performs these counts.  Here is a
+    sample ticky-ticky statistics file, generated by the invocation
+    <command>foo +RTS -rfoo.ticky</command>.</para>
+
+<screen>
+ foo +RTS -rfoo.ticky
+
+
+ALLOCATIONS: 3964631 (11330900 words total: 3999476 admin, 6098829 goods, 1232595 slop)
+                                total words:        2     3     4     5    6+
+  69647 (  1.8%) function values                 50.0  50.0   0.0   0.0   0.0
+2382937 ( 60.1%) thunks                           0.0  83.9  16.1   0.0   0.0
+1477218 ( 37.3%) data values                     66.8  33.2   0.0   0.0   0.0
+      0 (  0.0%) big tuples
+      2 (  0.0%) black holes                      0.0 100.0   0.0   0.0   0.0
+      0 (  0.0%) prim things
+  34825 (  0.9%) partial applications             0.0   0.0   0.0 100.0   0.0
+      2 (  0.0%) thread state objects             0.0   0.0   0.0   0.0 100.0
+
+Total storage-manager allocations: 3647137 (11882004 words)
+        [551104 words lost to speculative heap-checks]
+
+STACK USAGE:
+
+ENTERS: 9400092  of which 2005772 (21.3%) direct to the entry code
+                  [the rest indirected via Node's info ptr]
+1860318 ( 19.8%) thunks
+3733184 ( 39.7%) data values
+3149544 ( 33.5%) function values
+                  [of which 1999880 (63.5%) bypassed arg-satisfaction chk]
+ 348140 (  3.7%) partial applications
+ 308906 (  3.3%) normal indirections
+      0 (  0.0%) permanent indirections
+
+RETURNS: 5870443
+2137257 ( 36.4%) from entering a new constructor
+                  [the rest from entering an existing constructor]
+2349219 ( 40.0%) vectored [the rest unvectored]
+
+RET_NEW:         2137257:  32.5% 46.2% 21.3%  0.0%  0.0%  0.0%  0.0%  0.0%  0.0%
+RET_OLD:         3733184:   2.8% 67.9% 29.3%  0.0%  0.0%  0.0%  0.0%  0.0%  0.0%
+RET_UNBOXED_TUP:       2:   0.0%  0.0%100.0%  0.0%  0.0%  0.0%  0.0%  0.0%  0.0%
+
+RET_VEC_RETURN : 2349219:   0.0%  0.0%100.0%  0.0%  0.0%  0.0%  0.0%  0.0%  0.0%
+
+UPDATE FRAMES: 2241725 (0 omitted from thunks)
+SEQ FRAMES:    1
+CATCH FRAMES:  1
+UPDATES: 2241725
+      0 (  0.0%) data values
+  34827 (  1.6%) partial applications
+                  [2 in place, 34825 allocated new space]
+2206898 ( 98.4%) updates to existing heap objects (46 by squeezing)
+UPD_CON_IN_NEW:         0:       0      0      0      0      0      0      0      0      0
+UPD_PAP_IN_NEW:     34825:       0      0      0  34825      0      0      0      0      0
+
+NEW GEN UPDATES: 2274700 ( 99.9%)
+
+OLD GEN UPDATES: 1852 (  0.1%)
+
+Total bytes copied during GC: 190096
+
+**************************************************
+3647137 ALLOC_HEAP_ctr
+11882004 ALLOC_HEAP_tot
+  69647 ALLOC_FUN_ctr
+  69647 ALLOC_FUN_adm
+  69644 ALLOC_FUN_gds
+  34819 ALLOC_FUN_slp
+  34831 ALLOC_FUN_hst_0
+  34816 ALLOC_FUN_hst_1
+      0 ALLOC_FUN_hst_2
+      0 ALLOC_FUN_hst_3
+      0 ALLOC_FUN_hst_4
+2382937 ALLOC_UP_THK_ctr
+      0 ALLOC_SE_THK_ctr
+ 308906 ENT_IND_ctr
+      0 E!NT_PERM_IND_ctr requires +RTS -Z
+[... lots more info omitted ...]
+      0 GC_SEL_ABANDONED_ctr
+      0 GC_SEL_MINOR_ctr
+      0 GC_SEL_MAJOR_ctr
+      0 GC_FAILED_PROMOTION_ctr
+  47524 GC_WORDS_COPIED_ctr
+</screen>
+
+    <para>The formatting of the information above the row of asterisks
+    is subject to change, but hopefully provides a useful
+    human-readable summary.  Below the asterisks <emphasis>all
+    counters</emphasis> maintained by the ticky-ticky system are
+    dumped, in a format intended to be machine-readable: zero or more
+    spaces, an integer, a space, the counter name, and a newline.</para>
+
+    <para>In fact, not <emphasis>all</emphasis> counters are
+    necessarily dumped; compile- or run-time flags can render certain
+    counters invalid.  In this case, either the counter will simply
+    not appear, or it will appear with a modified counter name,
+    possibly along with an explanation for the omission (notice
+    <literal>ENT&lowbar;PERM&lowbar;IND&lowbar;ctr</literal> appears
+    with an inserted <literal>!</literal> above).  Software analysing
+    this output should always check that it has the counters it
+    expects.  Also, beware: some of the counters can have
+    <emphasis>large</emphasis> values!</para>
+
+  </sect1>
+
+</chapter>
+
+<!-- Emacs stuff:
+     ;;; Local Variables: ***
+     ;;; mode: xml ***
+     ;;; sgml-parent-document: ("users_guide.xml" "book" "chapter") ***
+     ;;; End: ***
+ -->