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