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MLton
20241230
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<h1>ProfilingTheStack</h1>
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<div class="paragraph">
<p>For all forms of <a href="Profiling">Profiling</a>, you can gather counts for all
functions on the stack, not just the currently executing function.  To
do so, compile your program with <code>-profile-stack true</code>.  For example,
suppose that <code>list-rev.sml</code> contains the following.</p>
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<pre class="rouge highlight"><code data-lang="sml"><span class="kr">fun</span> <span class="nf">append</span> <span class="p">(</span><span class="n">l1</span><span class="p">,</span> <span class="n">l2</span><span class="p">)</span> <span class="p">=</span>
   <span class="kr">case</span> <span class="n">l1</span> <span class="kr">of</span>
      <span class="p">[]</span> <span class="p">=&gt;</span> <span class="n">l2</span>
    <span class="p">|</span> <span class="n">x</span> <span class="n">::</span> <span class="n">l1</span> <span class="p">=&gt;</span> <span class="n">x</span> <span class="n">::</span> <span class="n">append</span> <span class="p">(</span><span class="n">l1</span><span class="p">,</span> <span class="n">l2</span><span class="p">)</span>

<span class="kr">fun</span> <span class="nf">rev</span> <span class="n">l</span> <span class="p">=</span>
   <span class="kr">case</span> <span class="n">l</span> <span class="kr">of</span>
      <span class="p">[]</span> <span class="p">=&gt;</span> <span class="p">[]</span>
    <span class="p">|</span> <span class="n">x</span> <span class="n">::</span> <span class="n">l</span> <span class="p">=&gt;</span> <span class="n">append</span> <span class="p">(</span><span class="n">rev</span> <span class="n">l</span><span class="p">,</span> <span class="p">[</span><span class="n">x</span><span class="p">])</span>

<span class="kr">val</span> <span class="nv">l</span> <span class="p">=</span> <span class="nn">List</span><span class="p">.</span><span class="n">tabulate</span> <span class="p">(</span><span class="mi">1000</span><span class="p">,</span> <span class="kr">fn</span> <span class="n">i</span> <span class="p">=&gt;</span> <span class="n">i</span><span class="p">)</span>
<span class="kr">val</span> <span class="nv">_</span> <span class="p">=</span> <span class="mi">1</span> <span class="n">+</span> <span class="n">hd</span> <span class="p">(</span><span class="n">rev</span> <span class="n">l</span><span class="p">)</span></code></pre>
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<p>Compile with stack profiling and then run the program.</p>
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<pre>% mlton -profile alloc -profile-stack true list-rev.sml
% ./list-rev</pre>
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<p>Display the profiling data.</p>
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<pre>% mlprof -show-line true list-rev mlmon.out
6,030,136 bytes allocated (108,336 bytes by GC)
       function          cur  stack  GC
----------------------- ----- ----- ----
append  list-rev.sml: 1 97.6% 97.6% 1.4%
&lt;gc&gt;                     1.8%  0.0% 1.8%
&lt;main&gt;                   0.4% 98.2% 1.8%
rev  list-rev.sml: 6     0.2% 97.6% 1.8%</pre>
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<p>In the above table, we see that <code>rev</code>, defined on line 6 of
<code>list-rev.sml</code>, is only responsible for 0.2% of the allocation, but is
on the stack while 97.6% of the allocation is done by the user program
and while 1.8% of the allocation is done by the garbage collector.</p>
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<p>The run-time performance impact of <code>-profile-stack true</code> can be
noticeable since there is some extra bookkeeping at every nontail call
and return.</p>
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Last updated Thu Oct 21 15:53:06 2021 -0400 by Matthew Fluet.
<a href="https://github.com/MLton/mlton/commits/master/doc/guide/src/ProfilingTheStack.adoc">Log</a>
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