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26 <h1>ProfilingTheStack</h1>
30 <div class="sectionbody">
31 <div class="paragraph"><p>For all forms of <a href="Profiling">Profiling</a>, you can gather counts for all
32 functions on the stack, not just the currently executing function. To
33 do so, compile your program with <span class="monospaced">-profile-stack true</span>. For example,
34 suppose that <span class="monospaced">list-rev.sml</span> contains the following.</p></div>
35 <div class="listingblock">
36 <div class="content"><div class="highlight"><pre><span class="k">fun</span><span class="w"> </span><span class="n">append</span><span class="w"> </span><span class="p">(</span><span class="n">l1</span><span class="p">,</span><span class="w"> </span><span class="n">l2</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
37 <span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">l1</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
38 <span class="w"> </span><span class="p">[]</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">l2</span><span class="w"></span>
39 <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">l1</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">append</span><span class="w"> </span><span class="p">(</span><span class="n">l1</span><span class="p">,</span><span class="w"> </span><span class="n">l2</span><span class="p">)</span><span class="w"></span>
41 <span class="k">fun</span><span class="w"> </span><span class="n">rev</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
42 <span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
43 <span class="w"> </span><span class="p">[]</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="p">[]</span><span class="w"></span>
44 <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">append</span><span class="w"> </span><span class="p">(</span><span class="n">rev</span><span class="w"> </span><span class="n">l</span><span class="p">,</span><span class="w"> </span><span class="p">[</span><span class="n">x</span><span class="p">])</span><span class="w"></span>
46 <span class="k">val</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">tabulate</span><span class="w"> </span><span class="p">(</span><span class="mi">1000</span><span class="p">,</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">i</span><span class="p">)</span><span class="w"></span>
47 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="n">hd</span><span class="w"> </span><span class="p">(</span><span class="n">rev</span><span class="w"> </span><span class="n">l</span><span class="p">)</span><span class="w"></span>
48 </pre></div></div></div>
49 <div class="paragraph"><p>Compile with stack profiling and then run the program.</p></div>
50 <div class="listingblock">
51 <div class="content monospaced">
52 <pre>% mlton -profile alloc -profile-stack true list-rev.sml
55 <div class="paragraph"><p>Display the profiling data.</p></div>
56 <div class="listingblock">
57 <div class="content monospaced">
58 <pre>% mlprof -show-line true list-rev mlmon.out
59 6,030,136 bytes allocated (108,336 bytes by GC)
61 ----------------------- ----- ----- ----
62 append list-rev.sml: 1 97.6% 97.6% 1.4%
63 <gc> 1.8% 0.0% 1.8%
64 <main> 0.4% 98.2% 1.8%
65 rev list-rev.sml: 6 0.2% 97.6% 1.8%</pre>
67 <div class="paragraph"><p>In the above table, we see that <span class="monospaced">rev</span>, defined on line 6 of
68 <span class="monospaced">list-rev.sml</span>, is only responsible for 0.2% of the allocation, but is
69 on the stack while 97.6% of the allocation is done by the user program
70 and while 1.8% of the allocation is done by the garbage collector.</p></div>
71 <div class="paragraph"><p>The run-time performance impact of <span class="monospaced">-profile-stack true</span> can be
72 noticeable since there is some extra bookkeeping at every nontail call
77 <div id="footnotes"><hr></div>
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