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148 lines
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<title>Flat Profile - GNU gprof</title>
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This file documents the gprof profiler of the GNU system.
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<p>
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<a name="Flat-Profile"></a>Next: <a rel="next" accesskey="n" href="Call-Graph.html#Call-Graph">Call Graph</a>,
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Up: <a rel="up" accesskey="u" href="Output.html#Output">Output</a>
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<hr><br>
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</div>
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<h3 class="section">5.1 The Flat Profile</h3>
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<p><a name="index-flat-profile-1"></a>
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The <dfn>flat profile</dfn> shows the total amount of time your program
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spent executing each function. Unless the <span class="samp">-z</span> option is given,
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functions with no apparent time spent in them, and no apparent calls
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to them, are not mentioned. Note that if a function was not compiled
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for profiling, and didn't run long enough to show up on the program
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counter histogram, it will be indistinguishable from a function that
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was never called.
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<p>This is part of a flat profile for a small program:
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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 ms/call ms/call name
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33.34 0.02 0.02 7208 0.00 0.00 open
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16.67 0.03 0.01 244 0.04 0.12 offtime
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16.67 0.04 0.01 8 1.25 1.25 memccpy
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16.67 0.05 0.01 7 1.43 1.43 write
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16.67 0.06 0.01 mcount
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0.00 0.06 0.00 236 0.00 0.00 tzset
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0.00 0.06 0.00 192 0.00 0.00 tolower
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0.00 0.06 0.00 47 0.00 0.00 strlen
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0.00 0.06 0.00 45 0.00 0.00 strchr
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0.00 0.06 0.00 1 0.00 50.00 main
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0.00 0.06 0.00 1 0.00 0.00 memcpy
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0.00 0.06 0.00 1 0.00 10.11 print
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0.00 0.06 0.00 1 0.00 0.00 profil
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0.00 0.06 0.00 1 0.00 50.00 report
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...
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</pre>
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<p class="noindent">The functions are sorted first by decreasing run-time spent in them,
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then by decreasing number of calls, then alphabetically by name. The
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functions <span class="samp">mcount</span> and <span class="samp">profil</span> are part of the profiling
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apparatus and appear in every flat profile; their time gives a measure of
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the amount of overhead due to profiling.
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<p>Just before the column headers, a statement appears indicating
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how much time each sample counted as.
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This <dfn>sampling period</dfn> estimates the margin of error in each of the time
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figures. A time figure that is not much larger than this is not
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reliable. In this example, each sample counted as 0.01 seconds,
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suggesting a 100 Hz sampling rate.
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The program's total execution time was 0.06
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seconds, as indicated by the <span class="samp">cumulative seconds</span> field. Since
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each sample counted for 0.01 seconds, this means only six samples
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were taken during the run. Two of the samples occurred while the
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program was in the <span class="samp">open</span> function, as indicated by the
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<span class="samp">self seconds</span> field. Each of the other four samples
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occurred one each in <span class="samp">offtime</span>, <span class="samp">memccpy</span>, <span class="samp">write</span>,
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and <span class="samp">mcount</span>.
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Since only six samples were taken, none of these values can
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be regarded as particularly reliable.
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In another run,
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the <span class="samp">self seconds</span> field for
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<span class="samp">mcount</span> might well be <span class="samp">0.00</span> or <span class="samp">0.02</span>.
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See <a href="Sampling-Error.html#Sampling-Error">Statistical Sampling Error</a>,
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for a complete discussion.
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<p>The remaining functions in the listing (those whose
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<span class="samp">self seconds</span> field is <span class="samp">0.00</span>) didn't appear
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in the histogram samples at all. However, the call graph
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indicated that they were called, so therefore they are listed,
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sorted in decreasing order by the <span class="samp">calls</span> field.
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Clearly some time was spent executing these functions,
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but the paucity of histogram samples prevents any
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determination of how much time each took.
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<p>Here is what the fields in each line mean:
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<dl>
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<dt><code>% time</code><dd>This is the percentage of the total execution time your program spent
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in this function. These should all add up to 100%.
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<br><dt><code>cumulative seconds</code><dd>This is the cumulative total number of seconds the computer spent
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executing this functions, plus the time spent in all the functions
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above this one in this table.
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<br><dt><code>self seconds</code><dd>This is the number of seconds accounted for by this function alone.
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The flat profile listing is sorted first by this number.
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<br><dt><code>calls</code><dd>This is the total number of times the function was called. If the
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function was never called, or the number of times it was called cannot
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be determined (probably because the function was not compiled with
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profiling enabled), the <dfn>calls</dfn> field is blank.
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<br><dt><code>self ms/call</code><dd>This represents the average number of milliseconds spent in this
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function per call, if this function is profiled. Otherwise, this field
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is blank for this function.
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<br><dt><code>total ms/call</code><dd>This represents the average number of milliseconds spent in this
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function and its descendants per call, if this function is profiled.
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Otherwise, this field is blank for this function.
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This is the only field in the flat profile that uses call graph analysis.
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<br><dt><code>name</code><dd>This is the name of the function. The flat profile is sorted by this
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field alphabetically after the <dfn>self seconds</dfn> and <dfn>calls</dfn>
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fields are sorted.
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</dl>
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</body></html>
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