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 first by decreasing run-time spent in them, then by decreasing number of calls, then alphabetically by name. The functions `mcount' and `profil' 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.
Just before the column headers, a statement appears indicating how much time each sample counted as. This 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, 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 `cumulative seconds' 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 `open' function, as indicated by the `self seconds' field. Each of the other four samples occurred one each in `offtime', `memccpy', `write', and `mcount'. Since only six samples were taken, none of these values can be regarded as particularly reliable. In another run, the `self seconds' field for `mcount' might well be `0.00' or `0.02'. See Statistical Sampling Error, for a complete discussion.
The remaining functions in the listing (those whose `self seconds' field is `0.00') 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 `calls' field. Clearly some time was spent executing these functions, but the paucity of histogram samples prevents any determination of how much time each took.
Here is what the fields in each line mean: