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>
+ flattened into a tree.</para>
<sect2><title>Inserting cost centres by hand</title>
<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>
currently support mixing the <option>-hr</option> and
<option>-hb</option> options.</para>
- <para>There are two more options which relate to heap
+ <para>There are three more options which relate to heap
profiling:</para>
<variablelist>
by closure description or type description.</para>
</listitem>
</varlistentry>
+
+ <varlistentry>
+ <term>
+ <option>-L<replaceable>num</replaceable></option>
+ <indexterm><primary><option>-L</option></primary><secondary>RTS option</secondary></indexterm>
+ </term>
+ <listitem>
+ <para>
+ Sets the maximum length of a cost-centre stack name in a
+ heap profile. Defaults to 25.
+ </para>
+ </listitem>
+ </varlistentry>
</variablelist>
</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><prog>.prof</filename>. To see the
- profile, run <command>ghcprof</command> like this:</para>
-
- <indexterm><primary><option>-px</option></primary></indexterm>
-
-<screen>
-$ ghcprof <prog>.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>––heap profile to PostScript</title>
</screen>
</para>
</sect2>
+ </sect1>
+
+ <sect1 id="hpc">
+ <title>Observing Code Coverage</title>
+ <indexterm><primary>code coverage</primary></indexterm>
+ <indexterm><primary>Haskell Program Coverage</primary></indexterm>
+ <indexterm><primary>hpc</primary></indexterm>
+
+ <para>
+ Code coverage tools allow a programer to determine what parts of
+ their code have been actually executed, and which parts have
+ never actually been invoked. GHC has an option for generating
+ instrumented code that records code coverage as part of the
+ <ulink url="http://www.haskell.org/hpc">Haskell Program Coverage
+ </ulink>(HPC) toolkit. HPC tools can be used to render the
+ outputed code coverage infomation into human understandable
+ format.
+ </para>
+
+ <para>
+ HPC provides coverage information of two kinds: source coverage
+ and boolean-control coverage. Source coverage is the extent to
+ which every part of the program was used, measured at three
+ different levels: declarations (both top-level and local),
+ alternatives (among several equations or case branches) and
+ expressions (at every level). Boolean coverage is the extent to
+ which each of the values True and False is obtained in every
+ syntactic boolean context (ie. guard, condition, qualifier).
+ </para>
+
+ <para>
+ HPC displays both kinds of information in two different ways:
+ textual reports with summary statistics (hpc-report) and sources
+ with color mark-up (hpc-markup). For boolean coverage, there
+ are four possible outcomes for each guard, condition or
+ qualifier: both True and False values occur; only True; only
+ False; never evaluated. In hpc-markup output, highlighting with
+ a yellow background indicates a part of the program that was
+ never evaluated; a green background indicates an always-True
+ expression and a red background indicates an always-False one.
+ </para>
+
+ <sect2><title>A small example: Reciprocation</title>
+
+ <para>
+ For an example we have a program which computes exact decimal
+ representations of reciprocals, with recurring parts indicated in
+ brackets. We first build an instrumented version using the
+ hpc-build script. Assuming the source file is Recip.hs.
+ </para>
+<programlisting>
+reciprocal :: Int -> (String, Int)
+reciprocal n | n > 1 = ('0' : '.' : digits, recur)
+ | otherwise = error
+ "attempting to compute reciprocal of number <= 1"
+ where
+ (digits, recur) = divide n 1 []
+divide :: Int -> Int -> [Int] -> (String, Int)
+divide n c cs | c `elem` cs = ([], position c cs)
+ | r == 0 = (show q, 0)
+ | r /= 0 = (show q ++ digits, recur)
+ where
+ (q, r) = (c*10) `quotRem` n
+ (digits, recur) = divide n r (c:cs)
+
+position :: Int -> [Int] -> Int
+position n (x:xs) | n==x = 1
+ | otherwise = 1 + position n xs
+
+showRecip :: Int -> String
+showRecip n =
+ "1/" ++ show n ++ " = " ++
+ if r==0 then d else take p d ++ "(" ++ drop p d ++ ")"
+ where
+ p = length d - r
+ (d, r) = reciprocal n
+
+main = do
+ number <- readLn
+ putStrLn (showRecip number)
+ main
+</programlisting>
+
+` <para>The HPC intrumentation is enabled using the -fhpc flag.
+ </para>
+<screen>
+$ ghc -fhpc Recip.hs --make
+</screen>
+ <para>HPC index (.mix) files are placed placed in .hpc subdirectory. These can be considered like
+ the .hi files for HPC. They contain information about what parts of the haskell each modules.
+ </para>
+<screen>
+$ ./Recip
+1/3
+= 0.(3)
+</screen>
+ <para>Now for a textual summary of coverage:</para>
+<screen>
+$ hpc-report Recip
+ 80% expressions used (81/101)
+ 12% boolean coverage (1/8)
+ 14% guards (1/7), 3 always True,
+ 1 always False,
+ 2 unevaluated
+ 0% 'if' conditions (0/1), 1 always False
+ 100% qualifiers (0/0)
+ 55% alternatives used (5/9)
+100% local declarations used (9/9)
+100% top-level declarations used (5/5)
+</screen>
+ <para>Finally, we generate a marked-up version of the source.</para>
+<screen>
+$ hpc-markup Recip
+writing Recip.hs.html
+</screen>
+<figure>
+ <title>Recip.hs.html</title>
+ <graphic fileref="images/Recip.png"></graphic>
+ </figure>
+ </sect2>
</sect1>
<sect1 id="ticky-ticky">
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 “Customising what libraries to build,” in
- the installation guide.</para>
+ have built the ticky RTS. (This should be described in
+ the building guide, but amounts to building the RTS with way
+ "t" enabled.)</para>
<para>To get your compiled program to spit out the ticky-ticky
numbers, use a <option>-r</option> RTS
projects / ghc-hetmet.git / blobdiff