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# How to Understand the Flat Profile

The flat profile shows the total amount of time your program spent executing each function. Unless the ``-z'` 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.

This is part of a flat profile for a small program:

    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
    ...

The functions are sorted by decreasing run-time spent in them. The functions ``mcount'` and ``profil'` are part of the profiling aparatus and appear in every flat profile; their time gives a measure of the amount of overhead due to profiling.

The sampling period 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, the ``self seconds'` field for ``mcount'` might well be ``0'` or ``0.04'` in another run. See section Statistical Inaccuracy of `gprof` Output, for a complete discussion.

Here is what the fields in each line mean:

`% time`
  This is the percentage of the total execution time your program spent in this function. These should all add up to 100%.
`cumulative seconds`
  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.
`self seconds`
  This is the number of seconds accounted for by this function alone. The flat profile listing is sorted first by this number.
`calls`
  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 calls field is blank.
`self ms/call`
  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.
`total ms/call`
  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.
`name`
  This is the name of the function. The flat profile is sorted by this field alphabetically after the self seconds field is sorted.

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