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<title>GNU gprof: Line-by-line</title>
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<a name="Line_002dby_002dline"></a>
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<div class="header">
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<p>
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Next: <a href="Annotated-Source.html#Annotated-Source" accesskey="n" rel="next">Annotated Source</a>, Previous: <a href="Call-Graph.html#Call-Graph" accesskey="p" rel="previous">Call Graph</a>, Up: <a href="Output.html#Output" accesskey="u" rel="up">Output</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
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<a name="Line_002dby_002dline-Profiling"></a>
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<h3 class="section">5.3 Line-by-line Profiling</h3>
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<p><code>gprof</code>’s ‘<samp>-l</samp>’ option causes the program to perform
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<em>line-by-line</em> profiling. In this mode, histogram
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samples are assigned not to functions, but to individual
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lines of source code. This only works with programs compiled with
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older versions of the <code>gcc</code> compiler. Newer versions of <code>gcc</code>
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use a different program - <code>gcov</code> - to display line-by-line
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profiling information.
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</p>
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<p>With the older versions of <code>gcc</code> the program usually has to be
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compiled with a ‘<samp>-g</samp>’ option, in addition to ‘<samp>-pg</samp>’, in order
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to generate debugging symbols for tracking source code lines.
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Note, in much older versions of <code>gcc</code> the program had to be
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compiled with the ‘<samp>-a</samp>’ command-line option as well.
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</p>
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<p>The flat profile is the most useful output table
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in line-by-line mode.
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The call graph isn’t as useful as normal, since
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the current version of <code>gprof</code> does not propagate
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call graph arcs from source code lines to the enclosing function.
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The call graph does, however, show each line of code
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that called each function, along with a count.
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</p>
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<p>Here is a section of <code>gprof</code>’s output, without line-by-line profiling.
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Note that <code>ct_init</code> accounted for four histogram hits, and
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13327 calls to <code>init_block</code>.
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</p>
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<div class="smallexample">
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<pre class="smallexample">Flat profile:
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Each sample counts as 0.01 seconds.
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% cumulative self self total
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time seconds seconds calls us/call us/call name
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30.77 0.13 0.04 6335 6.31 6.31 ct_init
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Call graph (explanation follows)
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granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds
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index % time self children called name
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0.00 0.00 1/13496 name_too_long
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0.00 0.00 40/13496 deflate
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0.00 0.00 128/13496 deflate_fast
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0.00 0.00 13327/13496 ct_init
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[7] 0.0 0.00 0.00 13496 init_block
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</pre></div>
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<p>Now let’s look at some of <code>gprof</code>’s output from the same program run,
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this time with line-by-line profiling enabled. Note that <code>ct_init</code>’s
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four histogram hits are broken down into four lines of source code—one hit
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occurred on each of lines 349, 351, 382 and 385. In the call graph,
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note how
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<code>ct_init</code>’s 13327 calls to <code>init_block</code> are broken down
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into one call from line 396, 3071 calls from line 384, 3730 calls
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from line 385, and 6525 calls from 387.
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</p>
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<div class="smallexample">
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<pre class="smallexample">Flat profile:
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Each sample counts as 0.01 seconds.
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% cumulative self
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time seconds seconds calls name
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7.69 0.10 0.01 ct_init (trees.c:349)
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7.69 0.11 0.01 ct_init (trees.c:351)
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7.69 0.12 0.01 ct_init (trees.c:382)
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7.69 0.13 0.01 ct_init (trees.c:385)
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Call graph (explanation follows)
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granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds
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% time self children called name
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0.00 0.00 1/13496 name_too_long (gzip.c:1440)
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0.00 0.00 1/13496 deflate (deflate.c:763)
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0.00 0.00 1/13496 ct_init (trees.c:396)
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0.00 0.00 2/13496 deflate (deflate.c:727)
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0.00 0.00 4/13496 deflate (deflate.c:686)
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0.00 0.00 5/13496 deflate (deflate.c:675)
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0.00 0.00 12/13496 deflate (deflate.c:679)
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0.00 0.00 16/13496 deflate (deflate.c:730)
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0.00 0.00 128/13496 deflate_fast (deflate.c:654)
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0.00 0.00 3071/13496 ct_init (trees.c:384)
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0.00 0.00 3730/13496 ct_init (trees.c:385)
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0.00 0.00 6525/13496 ct_init (trees.c:387)
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[6] 0.0 0.00 0.00 13496 init_block (trees.c:408)
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Next: <a href="Annotated-Source.html#Annotated-Source" accesskey="n" rel="next">Annotated Source</a>, Previous: <a href="Call-Graph.html#Call-Graph" accesskey="p" rel="previous">Call Graph</a>, Up: <a href="Output.html#Output" accesskey="u" rel="up">Output</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
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